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  < Back to Table Of Contents  < Back to Topic: Create & Innovate Plus Home Made Gifts & Games

article number 365
article date 07-31-2014
copyright 2014 by Author else SaltOfAmerica
We Invent to Improve Our Submarines
by Herbert Zim
   

From the 1942 book, “Submarines.”

ANCESTORS OF THE SUBMARINE

THE submarine is a comparatively new type of boat. It has only been under Construction for 5,000 years. That it should take so long to perfect the submarine is not unusual, since most of our important inventions had an even earlier start. The beginning of the submarine might go back to the time when one of our savage ancestors rolled off the log he was using for a boat, and discovered that his short and unexpected journey under water was not as dangerous or as terrifying as he had feared.

No one knows when man first learned to swim and dive. Scientists digging in ancient ruins, some 4,000 years old, have uncovered articles of pearl and mother of pearl that could only have been made from material gathered by people trained to dive and swim under water. These divers, going under water for a definite purpose, might be considered the most distant ancestors of the submarine.

Perhaps they should not be so considered until we know when the first diver got the idea of taking a stone with him to help him sink faster and to keep him on the bottom. When he wanted to return to the surface, he dropped the rock. Who this man was we shall probably never know, but he made practical use of the same principle now applied in a modern submarine.

Early progress was undoubtedly slow and the occasional stories and legends that have survived do not give detailed information. Early scientists, such as the famous Aristotle, wrote in their journals accounts of how men could work under water, breathing through a tube.

And it is clear that during the Greek wars about 400 B.C. divers equipped with some kind of artificial aid in breathing under water were able to cut the ropes that anchored the enemy’s ships.

There are other interesting early records, dating before the time of Christ, of divers who salvaged sunken ships. There is the quaint story of the descent of Alexander the Great under water in a tank or cage merely to observe the fish. It is recorded, with probably a slight exaggeration, that he saw one fish so large it took three days to swim past the cage.

   
PEARL DIVERS: THE FIRST SUBMARINERS.

By the Middle Ages progress had been made to the extent that people went below the surface of the water completely protected by diving bells and other devices. These pre-submarines were merely large pots or vessels that were sunk upside down. In them people could descend to the bottom and remain under water for some length of time.

These were at first mere curiosities, used in exhibitions to entertain royalty and the populace, but by 1600, the records tell us, it was proposed that diving bells have definite military use in “the recovery of artillery from the sea—as well as for other things.” After the English, with the timely aid of a heavy storm, sank the Spanish Armada, tales were circulated about vast wealth that was supposed to have been on board some of the ships. By 1650, with the use of diving bells, some old cannons were recovered from these boats, but there is no record of finding the gold.

About this period the true submarine was first being perfected. There are records that in 1620 Cornelius Drebel (sometimes called Van Drebel), a Hollander living in London, built himself a submarine boat of wood, and covered it with leather and tallow. This boat attracted the attention of King James I, who was supposed to have been a passenger in it during a trip down the Thames.

It is not clear how much this first submarine submerged, or whether it merely floated just under the surface of the water. One account states that it submerged 15 feet. This first submarine was propelled by a dozen rowers, and the records state that Drebel had in his submarine “a chemical liquor which would speedily restore to the air such a portion of vital parts as to make it again fit.”

If the records are true, this remarkable boat foreshadowed present submarines in more ways than one. It not only submerged but kept the air pure while under water. Drebel’s submarine attracted the attention of John Wilkins, a man of great ingenuity, who wrote at length on ways to improve Drebel’s invention.

His writings go into great detail. In them he lists five of “many advantages and conveniences of such a contrivance.” One of these advantages makes perfectly clear the role of the submarine in naval warfare. Three hundred years ago John Wilkins said: It [the submarine] may be of very great advantage against a navy of enemies, who by this means may be undermined in the water and blown up.”

It did not take quite a hundred years for Wilkins’ prediction to be fulfilled. The first important attempt to use a submarine in warfare was during our own Revolutionary War. In 1776 an American, David Bushnell, built a one-man undersea craft and navigated it in the Hudson River. He conceived the idea of blowing up a British battleship by anchoring a bomb to its hull under water.

A time-bomb was attached to the outside of Bushnell’s boat and a screw was so arranged that it could be turned from within. Bushnell’s assistant managed to get under the British battleship ‘Eagle,’ anchored in New York harbor, and attempted to attach the bomb, but as the time passed rapidly and the moment for the explosion drew closer, he could not get the screw to penetrate the copper plating over the oak timbers of the enemy ship.

At last, with but a little time left, he cast off the bomb and made his escape. He had scarcely reached safety when there was a huge explosion near the warship but not close enough to do damage.

   
BUSHNELL’S “TURTLE,” USED DURING THE REVOLUTIONARY WAR, WAS THE FIRST PRACTICAL SUBMARINE.

Bushnell was rewarded by Washington for his courage, and later experimented further with his submarine. He was first to apply the idea of a screw propeller to the undersea boat. This screw propeller was turned by hand but was more convenient and efficient than oars. Bushnell’s Turtle was really the first practical submarine.

Another American who continued the development of the submarine was Robert Fulton, better known for designing the first successful steamboat. About ten years before Fulton sailed the ‘Clermont’ up the Hudson River to the surprise of scoffers who jeered at “Fulton’s Folly,” he was in France working on a submarine.

This boat, in form and structure, was somewhat like the submarine of today. The ‘Nautilus’ was long, oval in shape; it had a keel for balance, a rudder, and a screw propeller. It was equipped with a sail for use on the surface. There was a conning tower with a window for the pilot.

The hull was covered with plates of copper. Though Fulton was interested in the steam engine, he did not apply power to his undersea boat. The screw propeller was turned by hand.

We are told that Fulton offered his submarine to Napoleon, who witnessed a trial of it near Brest in 1801. Napoleon did not accept Fulton’s offer, neither did the British nor the American governments—all of whom thought that such a boat could serve no practical purpose in peace or war. Fulton left his submarine experiments and turned his attention to the steamboat.

   
ROBERT FULTON’S NAUTILUS” TRAVELED BY SAIL ON THE SURFACE. ON SUBMERGING, THE SAIL FOLDED DOWN AND A HANDTURNED PROPELLER WAS USED.

Soon after, another attempt was made to construct a submarine with the idea of using it to rescue Napoleon then in exile at St. Helena. It was designed by an Englishman named Johnson and was 100 feet long. Much mystery surrounds this boat, which was never used. Napoleon died before it was completed.

The work of Fulton and his contemporaries brings an exciting period of submarine development to a close. In its outer form and from a practical angle, the submarine had become established. It was as good as the brains, skill, and materials of the time could make it.

Only one thing remained—the application of power to propel the undersea craft. Not until about 80 years later was this next step taken, leading up to the period of modern submarine construction.

THE COMING OF THE MODERN SUBMARINE

AT the time of the Civil War, inventors were experimenting with small hand-propelled submarines carrying crews of not more than six
to eight men. It was such a submarine, the ‘David,’ that sailed out into the Charleston, S. C., harbor in February 1864 and succeeded in sinking the ‘U.S.S. Housatonic.’

Thus the United States Navy was the victim of the first successful submarine attack. But the submarine did not escape. A flood of water poured into an open hatch, sinking the boat and drowning her crew. During the Civil War both sides built submarines and semi-submarines. None of these was very successful.

Nearly sixty years had gone by since Fulton built a practical submarine. Since that time little progress had been made in the design and construction of undersea boats. This was largely due to the fact that no satisfactory source of power had been devised, and hand-propelled models were, of necessity, limited.

In 1880 an Englishman, Garrett by name, built a steam-propelled submarine. Realizing that it was impossible to fire the boilers while the boat was submerged, Garrett hit upon an ingenious way of overcoming the difficulty. A collapsible smokestack connected to his boiler.

The submarine steamed along the surface with fires roaring and smoke pouring from the stack till the boiler was filled with steam. When the steam pressure in the boiler had reached the safety limit, the collapsible smokestack was hastily lowered and fitted with a water-tight cover. The doors of the boiler were sealed air-tight, the hatches closed, and the submarine went under.

The steam that had accumulated in the boiler was sufficient to drive Garrett’s boat a number of miles under water. When the pressure became low it was necessary to come to the surface, hoist up the stack, and re-fire the boiler. Garrett made several successful submarines.

About this time another submarine was built by a Swedish inventor named Nordenfelt, who also designed guns. This boat was 64 feet long and could submerge to a depth of 50 feet. It was powered by a steam engine connected to twin screw propellers.

Nordenfelt included one of the first practical torpedo tubes in his boat, thus for the first time making the submarine the dangerous weapon it is today. The torpedo itself was invented by an Englishman, Whitehead, several years before. Nordenfelt’s designs influenced later builders of the submarines.

   
NORDENFELT SUBMARINE. HIS DESIGNS INFLUENCED LATER BUILDERS.

During this period electrical machinery was being improved. Practical generators, batteries, and motors became available for the first time. It was only natural that attempts were made to use electrical power for submarines.

In many ways the all-electric submarine is an ideal boat, especially when submerged. The fuel problem is eliminated. So is the danger from poisonous exhaust gases. Electric motors run silently and need only a minimum of attention.

In 1886 two Englishmen, Campbell and Ash, developed the first all-electric submarine. Power was produced by a battery of about 100 cells that drove two electric motors. The combined output of these motors was nearly 100 horse power—about that of a modern six cylinder car.

This all-electric submarine could travel at a speed of approximately seven miles an hour and could run a distance of nearly 80 miles before the batteries had to be recharged. The need for frequent charging and overhauling of inefficient batteries limited the cruising range and usefulness of the first electric submarine. Even with better batteries an all-electric would be impractical except for harbor defense.

The gasoline motor at this time was also being developed for the “horseless carriage.” While the steam submarine and electric submarine were proving unsatisfactory, gasoline engines were being built for submarine use. These engines were lighter in weight and developed greater horse power than steam engines.

By 1895 submarines propelled by two-cylinder, 45-horse power gasoline engines were traveling at speeds of six miles an hour. But the fumes produced by the gasoline engine and the poisonous gases in the exhaust prevented the use of the motor while the boat was submerged.

Even if it were possible to dispose of these gases, no submarine could carry a sufficient air supply for both the crew and the gasoline engines when submerged.

It became evident to submarine designers that the combination of a gasoline engine for surface travel and for recharging batteries, and an electric motor for undersea travel formed a combination that might best solve the problem of power for the submarine. Until 1910 this combination was widely used. In France two inventors worked on the problem and perfected the best combination power units of the period. Many early French submarines followed their design.

An Irish born American inventor, John P. Holland, was also working on submarines. He built his first experimental ship in 1875. Twenty years later he perfected his designs to such an extent that they were accepted by the U. S. Navy. For the navy Holland built the ‘Plunger’ in 1895. This boat was to be powered by steam and electricity. Before it was completed, Holland discovered that the designs were impractical, and he started anew.

By 1900 he completed the boat named after himself, which proved satisfactory after trials. Improvements were made and the navy ordered six of the ‘Holland’ X boats to be built at a cost of $170,000 each. Shortly after, five other boats were built for the British navy based on Holland’s design. The first of these was launched in 1901 in England under the supervision of a captain of the U. S. Navy.

   
U.S.S. “HOLLAND,” ONE OF THE FIRST U. S. SUBMARINES. THE TORPEDO TUBE MAY BE SEEN AT THE BOW AND ALSO AN INLET VALVE THROUGH WHICH THE BALLAST TANKS WERE FLOODED. Courtesy of U. S. Navy Recruiting Bureau.

About the same time another American, Simon Lake, was independently working on the submarine. He built an experimental boat that he operated in Chesapeake Bay. About 1895 he built another boat, 14 feet long, of pine, canvas, and sheet iron. This boat was mounted on wheels so that it could run on shallow bottoms. The propeller was hand-operated.

This boat operated successfully and received a good deal of attention.

Later Lake designed the ‘Argonaut,’ of similar construction. Lake’s boat was specifically planned for operation on the bottom. When the ballast tanks were filled, the boat sank on an even keel until it reached bottom. Then it moved around on wheels attached to the hull. This design made the boat very stable but limited its usefulness.

The Holland boat, on the other hand, was a true submarine. It could dive from the surface and maintain itself at various depths. However, this boat lacked stability and the early models were difficult to control.

It was soon evident to naval officials that neither the Holland nor the Lake submarine was completely satisfactory, but that a practical boat might be built embodying the best features of both. All modern submarines, in design, may be traced back to the work of these two American inventors.

The first naval submarines were Holland boats only 63 feet long with a beam (width) of 12 feet. They weighed 104 tons and were easily lifted out of the water by large cranes. They were powered by a four-cylinder engine—something like that of a Model T Ford.

The fumes from these engines were so bad that white mice were kept hanging in a cage near by. As long as the mice were frisky, the crew was safe. When the fumes got so bad that the mice were asphyxiated, the captain immediately got the crew out on deck.

The danger to battleships from these early pocket-sized boats was quickly recognized by the famous Admiral Dewey, who wrote during the Spanish-American War, when submarines became practical weapons: “If the Spaniards had had two such boats (Holland submarines) at Manila, I should have been unable to hold the Bay with the squadron I had.”

The term U-boat was a word that struck terror among all sailors during the early days of the First World War. The first U-boat, however, was built ten years before the war started. In 1904 the Krupp Shipbuilding Works at Kiel, Germany, built for the German navy the first of a series of undersea boats.

Conspicuous on the conning tower was the identification mark “U-1,” the U standing for ‘Untersee Bote,’ the German for submarine. It was this U that gave the U-boat its name. Today the term U-boat is still used.

   
U.S.S. “PLUNGER,” AN EARLY U. S. SUBMARINE. Courtesy of U. S. Navy Recruiting Bureau.

The U-1 was powered by two six-cylinder gasoline engines, producing a total of 400 horse power. These were connected to twin screws. The maximum speed of the U-1 was eleven knots.

Two years later the U-2 was designed, similar in construction but with more powerful engines. These developed 600 horse power and a speed of thirteen knots. Continual improvement on these two boats led to the U-3, U-4, U-5, and to the U-18 by 1910. By this time the horse power had increased to 1,400.

These U-boats were all powered by gasoline engines, using electricity from batteries when submerged. In 1910 the first Diesel engines were installed in the U-19. These were two six-cylinder engines producing 1,700 horse power and giving the boat a speed of 15 knots.

By 1911 improved Diesel engines gave both increased power and speed. At the same time, size of the submarine was being increased and details perfected, so that the boats at the beginning of the First World War were quite similar to the submarines of today, though much smaller in size.

At the same time that this feverish activity was going on in Germany in preparation for war, similar work was starting in the shipyards of England, France, and the United States. By the beginning of the First World War, the submarine had been developed as a powerful weapon of surprise attack.

Germany had already perfected several distinct types of submarines for specialized work. The UB type, with a submerged displacement of 650 tons, was designed for coastal work to attack enemy shipping. The UC type was slightly smaller and was especially designed to act as a mine-layer.

During the war several new forms of submarines were developed, including a British attempt—a large steam-driven submarine. By 1918 the major warring nations had all developed a number of types of undersea craft. There were small boats capable of maneuvering in difficult situations, as well as larger cruising submarines and mine-laying craft.

The depot ship was developed as a means of refueling and maintaining flotillas of submarines at sea. To all intents and purposes the modern submarine had arrived.

To deal carefully with the characteristics of each type of submarine developed from First World War days to the present would require an encyclopedic volume. The following table will give you a rough idea of the growth of the submarine from 1895 to the end of the First World War. Only a few types have been selected, and these for the sole purpose of showing the major changes that have taken place.

   
Specifications regarding the growth of the submarine from 1895 to 1919. Length, surface and submerged displacement, surface and submerged speed, cruising radius, surface and submerged horsepower, number of torpedo tubes.

The changes in the submarine since the First World War have not been basic changes. Practically every feature of the submarine has been modified and improved, but no drastic changes have been made except the addition of a submarine escape device through which the crew of a sunken submarine may have a chance to reach the surface safely. Communication devices and armament have been steadily improved.

Modern American submarines vary in length from 175 feet to over 300 feet. Most are able to dive to a depth of 300 feet or more. The surface speed varies from thirteen to over twenty knots. Their cruising range has been greatly increased, as has the power of their Diesel engines.

Armament on modern submarines includes deck guns as well as torpedo tubes. Some are equipped for mine-laying, and a few experimental models have been made to carry airplanes. Many of the details in the development and perfection of the submarine and its armament are military secrets and are closely guarded by the countries that have perfected them.

Since the problems of building and using submarines are well known, there is little chance that one country has made any startling or revolutionary change in its submarines of which other countries are ignorant.

Recent events make it only too clear that the submarine is still a very effective weapon of war. In spite of improved means of detecting submarines and combating them, the undersea boat is still an enemy to be feared. Because of their size submarines can now operate thousands of miles from their bases. They can carry their attack right into the enemy’s front door.

German submarines have sunk scores of tankers off our Atlantic coast. They have shelled West Indies ports. Japan has shelled a Pacific coast oil refinery. In return American submarines have successfully operated in the Atlantic and close to Tokio.

   
   
LAUNCHING OF THE “HADDOCK,” A 300 FOOT STREAMLINED SUBMARINE. From Press Association, Inc.
   
MODERN U. S. SUBMARINES AT THEIR BASE. Courtesy of U. S. Navy Recruiting Bureau.

PRINCIPLES OF THE SUBMARINE

A FEW simple facts about water are all that are needed to understand the problem of submerging and surfacing submarines. Two principal facts are obvious. First, water is a fluid; second, water has weight. Because water is a fluid, it completely lacks rigidity. It is free to flow and move. It will fill any space and crack into which it can flow— anything from a bucket to an ocean basin.

The reverse is also true. When something is placed in water, the water will be pushed aside and will flow away making room for the object being submerged in it. Once the flow of water has stopped, it again becomes balanced. It is in a state of equilibrium. If disturbed, it will flow until the balance is re-established.

While there is some flow of water in the ocean because of currents and temperature differences, practically speaking the ocean is a large body of water in a state of balance. When water is in such a state, the pressure it exerts against objects submerged in it varies with the depth.

If a sheet of cardboard, having an area of one square foot, is placed one foot below the surface of the ocean, it is under the pressure of the one cubic foot of water that rests upon it. If the square foot of cardboard is submerged to the depth of two feet, then two cubic feet of water press upon it, and so on to any depth.

   
PRESSURE VARIES WITH DEPTH. A SQUARE FOOT BOARD, ONE FOOT BELOW THE SURFACE WOULD BE UNDER THE PRESSURE OF A CUBIC FOOT OF WATER; AT THREE FEET BELOW THE SURFACE IT WOULD BE UNDER THE PRESSURE OF THREE CUBIC FEET OF WATER. A CUBIC FOOT OF SALT WATER WEIGHS 64 POUNDS.

You can see for yourself that the pressure under water increases with the depth, by getting a large tin can and punching three or four nail holes in the side, about an inch apart from bottom to top. Hold the can over a sink and fill it with water.

As the water spurts through the nail holes in the side of the can, notice that the stream from the lowest hole spurts the farthest. The stream from the second hole is weaker, and the stream from the highest hole is just a dribble. The greater the pressure, the farther the water will shoot out from the can.

   
WATER SPURTS FARTHEST FROM THE LOWEST HOLE IN THE CAN BECAUSE THERE IS MORE WATER ABOVE THIS HOLE AND HENCE THE PRESSURE THERE IS GREATEST.

Because water is a fluid, it does not make any difference which way the cardboard or any other object is turned under water. The pressure at the “average depth” of the object would be the same. Fluids have the property of transmitting pressure equally in all directions. This can be easily shown.

Tie a piece of rubber balloon over the end of a small funnel. The funnel is connected to a length of glass tubing by means of a short rubber tube. A small amount of colored water placed in the glass tube acts as indicator. When the funnel is gradually lowered beneath the surface of the water, the pressure on the bottom membrane of the balloon will be transmitted to the water in the tube.

As you move the funnel farther down, the pressure will increase, pressing the air in the funnel and forcing the colored water up the tube. This again shows that pressure increases with depth.

If the funnel is held stationary at any depth and turned so that it faces to any side, up or down, but always at the same level, the pressure will not change. In whatever direction the funnel is pointed, there will be the same pressure at a given depth.

   
BECAUSE WATER IS A FLUID, THE PRESSURE AT ANY DEPTH BENEATH THE SURFACE IS TRANSMITTED IN ALL DIRECTIONS. THIS DEVICE MEASURES THE PRESSURE IN FOUR DIRECTIONS AT THE SAME DEPTH.

Everyone understands that water has weight, but few people realize how heavy water really is. A pint of water weighs about a pound; a gallon, 8 pounds. A cubic foot of water, enough to fill a box measuring one foot on each side, weighs 62 1/2 pounds. Since ocean water contains salt and other chemicals, the weight of a cubic foot of ocean water is more—64 pounds.

One square foot of cardboard, placed one foot beneath the surface of the ocean, will be under the pressure of one cubic foot of water, weighing 64 pounds. At two-foot depth the pressure doubles, becoming 128 pounds; at 10 feet, it will be 640 pounds.

Since submarines must be made to withstand safely the pressure at depths of 200 to 300 feet, they must be strong enough to resist water pressure of from 13,000 to 20,000 pounds (6 to 10 tons) per square foot. If you consider the amount of surface on a submarine, the total pressure, when fully submerged, is enormous.

When a solid object is submerged under water, the pressure on the top of it will differ from the pressure on the bottom. If one could take a piece of rock, cut exactly to one cubic foot, and submerge it under ocean water to a depth of one foot, the pressure on the square foot forming the top surface of the rock would be 64 pounds.

Since the rock is a foot thick, the bottom of the rock would be two feet below the surface. Hence the pressure on it would be 128 pounds. The net result is that the rock is affected by these two different pressures; a pressure on top of 64 pounds and on the bottom of 128 pounds. The upward pressure is 64 pounds greater than the downward. For this reason, the rock seems to be lifted upward or pushed toward the surface with a force of 64 pounds.

This can easily be seen if the rock could be weighed on a scale and weighed again when hanging under water. A cubic foot of rock weighs about 150 pounds. Under water it would weigh only 86 pounds. It would make no difference how far under water the rock was placed, the pressure on the bottom would always be one foot greater than the pressure on the top, and on a square foot of surface this comes to 64 pounds.

   
Visualization of pressures on a rock of one cubic foot placed one foot under water.

Because any solid takes up room, it seems to lose weight when submerged in a fluid. This loss of weight is due to the fact that there are differences in pressure on the upper and lower surfaces of a submerged object. The submerged object is lifted or buoyed up by a force equal to the weight of the water it displaces (or pushes aside) when it is submerged.

The cubic foot of rock displaces a cubic foot of water when submerged, and hence is buoyed up by the weight of one cubic foot of water or 64 pounds. If the volume of the rock was two cubic feet, it would be buoyed up by a force of 128 pounds. Since a submarine displaces a great deal of water when it submerges, there is a strong force pushing it toward the surface.

It is this relation between the weight of an object and the weight of the water it displaces when submerged, that determines whether the object will sink or float. If an object weighs less than the water it displaces, it will float. If it weighs more, it will sink.

This may also be expressed in terms of weight and volume, since the volume of the submerged object and the volume of the water displaced are exactly the same. The volume of the water displaced (in cubic feet) multiplied by 64 (weight of a cubic foot of ocean water) will, of course, give you the weight of the water displaced.

If a man weighing 180 pounds is big enough to displace three cubic feet of water, he will float, as his weight will be less than the weight of water displaced. The weight of 3 cubic feet of water (3 x 64) is 192 pounds. If a man weighed 200 pounds and displaced three cubic feet of water, he would sink.

The same is true of a submarine. If a submarine weighs less than the water it displaces, it will float. If it is heavier, the submarine will sink.

The weight of the water displaced is determined entirely by the volume of the submarine, and that is fixed once and for all when the submarine is built and the steel plates are welded into place.

Since the volume or displacement of the submarine cannot be changed, its rising or sinking must be due to changes in weight alone.

These changes in weight are easily accomplished. Water is allowed to flood tanks in the submarine, thus increasing its weight. When the weight is increased until the submarine weighs more than the weight of the water displaced, the submarine will sink. In order to rise, the water is forced out of the tanks by compressed air, lightening the submarine until it weighs less than the water displaced.

   
THE P-2, A MODERN U. S. SUBMARINE, IS SURFACING AFTER DIVING PRACTICE. Courtesy of U. S. Navy Recruiting Bureau.

In a very simple way, this is the explanation of the submarine. It represents a discovery made by the famous Greek, scientist and mathematician, Archimedes, who lived about 200 B.C.

In practice, however, diving a submarine and getting it to the surface are far more complicated. Besides displacement, there are many other factors to be considered, though displacement is the most important. One of the facts that must be considered is the kind of water in which the submarine is sailing. Ocean water weighs 64 pounds per cubic foot; fresh water 62¼ pounds.

If a submarine dives in a river, it will have to take less water in its tanks to gain sufficient weight to submerge, since river water is lighter than ocean water. When a submarine floats on the surface of fresh water, it does not float as high because the buoyancy of fresh water is less, due to its lighter weight.

So far we have not spoken about floating objects. Since a good part of the time the submarine floats on the surface, like any other boat, we might consider this for a moment. When floating, of course, the submarine weighs less than the amount of water it would displace if submerged.

The submarine sinks into the water until it displaces a weight of water equal to its own weight. A submarine weighing 2,000 tons will sink until it displaces 2,000 tons of water.

If the captain desires the submarine to float lower down in the water, he can order the ballast tanks partly flooded. This will increase the weight of the submarine and it will sink until an equal weight of water is displaced.

Thus by regulating the amount of water in ballast tanks, the submarine can be made to float at different levels—with its decks clear of the water, with its decks awash, with its conning tower exposed. It can sink until only the periscope is showing, and can cruise at this depth.

   
U. S. SUBMARINE CRUISING AT PERISCOPE DEPTH. Courtesy of U. S. Navy Recruiting Bureau.

Thus by changing the weight of the submarine, the captain not only determines whether the boat will float or sink but actually controls the floating, so that the submarine will settle to any required depth. Since the volume of the submarine is fixed, the adjustment of weight becomes very important.

There are a number of ballast and trimming tanks in the submarine, each of which may be flooded separately. The captain can keep the boat level, tilted up, or tilted down, depending on the amount of water he floods into the different tanks. The application of these principles to the actual submerging of the submarine requires great skill and careful judgment. Exactly how this is done we will now consider in more detail.

PRACTICE OF DIVING

THE principle of buoyancy is the basic principle of submarine operation. Yet in the practical task of diving and surfacing much more
is involved. A ship lighter than the water it displaces can at best only be forced under the water for a short period of time. It would bob up again almost immediately.

Besides buoyancy the speed of the submarine is important. So is the trim and balance.

Submariners prefer to talk of three kinds of buoyancy or, perhaps it would be better to say, three conditions of buoyancy. They speak of positive buoyancy—when the submarine is lighter than the water it displaces and the total forces acting upon it push it toward the surface.

Negative buoyancy is just the opposite: The submarine weighs more than the water it displaces and the force of gravity is stronger than the lifting force. This pushes the submarine downward, and under negative buoyancy the submarine will continue to go down till it hits bottom.

In neutral buoyancy the submarine weighs exactly as much as the water it displaces. Hence it will float or remain stationary at whatever depth it happens to be. At this buoyancy it can easily be maneuvered up or down.

   
A SUBMARINE IN POSITIVE BUOYANCY IS LIFTED TO THE SURFACE BY THE FORCES ACTING ON IT. IN NEGATIVE BUOYANCY IT IS FORCED TOWARD THE BOTTOM. IN NEUTRAL BUOYANCY IT REMAINS STATIONARY BECAUSE THE FORCES OF BUOYANCY AND GRAVITY ARE BALANCED.

The submerging of the submarine, of course, involves a rapid change from positive to negative buoyancy—but not a complete change. If this occurred the submarine would sink so fast that it would be out of control.

In diving, the submarine is rarely in strong negative buoyancy. If the ballast tanks are so filled that neutral buoyancy is achieved, the hydroplanes will easily force the ship down. Thus it is advantageous for the submarine captain, especially while on war patrol, to have the ship in as near neutral buoyancy as possible.

Cargo and passenger ships are built with a large reserve buoyancy. This is the reason they can be heavily loaded with cargo and still have enough positive buoyancy to remain safely afloat, though they do sink lower in the water.

Submarines are not built with a large positive reserve buoyancy. The reserve buoyancy for U. S. submarines runs from 20% for the O-class to 25% for the S-1 boats. These are average figures but they may be almost considered theoretical since they would apply only to unloaded submarines.

As soon as the fuel supply is taken on board the weight of the submarine may increase from 50 to 200 tons. Food, stores, ammunition, torpedoes, and the crew itself increase the weight of the submarine so that the reserve buoyancy is lowered.

Even political conditions affect the reserve buoyancy. In wartime a submarine is kept more heavily loaded, giving it these advantages: first, it lies lower in the water and hence presents less silhouette to an enemy; second, it is easier to submerge; third, it is always in diving trim and ready to depart for duty immediately on receipt of orders.

A submarine with larger reserve buoyancy is a safer boat. In case of accidental sinking when one or two compartments may be flooded, a ship of higher reserve buoyancy may still have a chance to reach the surface.

By blowing all the tanks the submarine may be forced to rise in spite of the flooded compartments. One early submarine escaped in this way. Blowing the tanks was not enough, but the crew were able to drop overboard bar after bar of lead ballast till the ship rose.

When fully loaded, the reserve buoyancy on a submarine may be as low as 15%. This may be the condition of a ship fully loaded with fuel, supplies, and arms, as it leaves for patrol duty. While on patrol, fuel will be used up; so will food. If an enemy is encountered, the submarine will weigh about a ton less for each torpedo fired.

These changes will obviously lighten the boat, making it float higher. It is conceivable that in this way a submarine could be so lightened that it would not submerge when its main ballast tanks were flooded.

It is, therefore, an important task to keep the weight of a submarine constant and equally distributed, so no unpredictable factor will enter into its diving performance. This constancy is achieved by adding water to the trimming tanks to replace material consumed.

Fuel is the largest item for which compensation must be made. This is done automatically. Fuel is stored in a large number of tanks on board, perhaps eight or more, arranged in several groups in different parts of the ship. As the fuel is used by the Diesels, sea water automatically enters the fuel tanks and replaces the fuel.

The fuel oil is, of course, lighter than water. Since the water enters through the bottom of the tank, the fuel floats above it. Furthermore, the pressure of the water forces the fuel back to the Diesels.

   
WATER FLOWS INTO THE FUEL TANKS AS THE OIL FLOWS OUT. THIS AUTOMATICALLY COMPENSATES FOR THE WEIGHT OF THE OIL.

However, fuel and water do not have the same weight. A cubic foot of Diesel oil weighs 54 lbs. while a cubic foot of water weighs 64 lbs. If a tank has a capacity of 100 cubic feet, it will be 1,000 lbs. heavier when filled with sea water than when filled with Diesel oil. This factor must also be taken into account when making compensations.

Compensating for other losses or gains in weight is made possible by the variable ballast tanks built into the submarine in addition to the main ballast tanks. These variable tanks are located in the bow, the stern, and amidships. The function of these variable ballast tanks is to maintain the required trim and balance of the submarine.

When a submarine is first commissioned, a series of test dives is made with different amounts of water in the main and variable ballast tanks. The captain soon determines just how much water should be kept in the variable ballast tanks.

Thus he can easily ascend and descend by flooding only the main ballast tanks. Hence the variable ballast tanks are never completely full and never completely empty. The amount of water in them is changed to compensate for food or ammunition used up.

But diving or surfacing is done only with the main ballast tanks. The variable ballast tanks are not flooded at each dive.

   
MODERN U. S. SUBMARINE SUBMERGING ON A TRIAL RUN. Courtesy of U. S. Navy Recruiting Bureau.

To determine the amount of compensation, both weight and position must be considered. The submarine acts like an enlarged see-saw. A small weight at the bow or stern may act with a greater force than a large weight amidships.

One thousand gallons of fuel taken from a bow tank might tilt the bow up appreciably and make diving difficult. The same amount of fuel used from tanks amidships would have a lesser effect on the boat.

The true effect of any changes in weight on board the submarine is best measured by the sum of the weight, multiplied by the distance over which it acts. This distance is measured from the center of gravity of the ship, which is usually at the conning tower or a short distance astern.

A 100 pound weight added to the submarine at a distance 100 feet forward of the center of gravity would act on the ship with a force of 10,000 foot-pounds (100 feet x 100 lbs.). The same weight if added ten feet from the center of gravity would only subject the submarine to a force of 1,000 foot-pounds (10 feet X 100 lbs.).

The principle involved in this is exactly the same principle that applies to levers. For our purposes a submarine may be considered a long lever, balanced at the center of gravity.

The captain has a table on board that shows the percentage compensation for weight added or removed from any part of the ship. A careful record is kept of the weight of all fuel and supplies received on board a submarine.

   
MEN AT DIVING STATIONS IN A BRITISH SUBMARINE. DIALS INDICATE FLOODING OF VARIOUS BALLAST TANKS. NOTICE VENTILATING DUCTS ALONG CEILING. British Official Photograph—Crown Copyright Reserved.

The diving officer knows the feel of the ship so well that he can recognize instantly if the ship is off trim, and can make adjustments through the variable ballast tanks. His judgment is so accurate that he can detect differences of only a few hundred pounds in a four million pound submarine.

Once the trim has been adjusted by the variable ballast tanks, flooding the main ballast tanks will cause the ship to submerge; blowing these tanks will cause it to surface. Under these conditions the ship will sink at an even keel whether its engines are going or not. While this method of submergence is basic, it can be greatly speeded up by the use of hydroplanes and the forward speed of the ship.

The hydroplanes or diving rudders are flat wing-like structures that project on either side of bow and stern when in use. When the submarine is on the surface, the bow planes are usually rigged into a housing on the side of the hull. The hydroplanes are fitted to heavy shafts, and may be tilted from horizontal to an angle of about 30 degrees by turning two large control wheels in the central operating compartment.

   
AN OLD COASTAL-TYPE SUBMARINE. THE FORE-HYDROPLANES ARE RIGGED FOR DIVING. Courtesy of U. S. Navy Recruiting Bureau.

In diving, the hydroplanes are tilted as the ballast tanks are flooded. The bow hydroplanes are tilted forward. The rush of water against these hydroplanes forces the bow of the submarine under. The stern hydroplanes are tilted backward. The pressing of water against these tends to tilt the stern up and hence forces the bow under faster.

Two factors are involved in this operation. One is the speed of the submarine. The second is the degree of tilt on the hydroplanes.

While it might seem logical to tilt the planes at a strong angle and force the submarine down quickly, this is impractical for several reasons. If the bow goes down at too steep an angle and too quickly, the stern will be raised out of the water. Then the propellers will spin violently in the air. This is not only dangerous for the propellers but cuts the speed necessary for diving.

Hence a submarine dives at the low angle of 2 or 3 degrees and usually less than 5 degrees.

Diving at a steep angle makes the ship harder to control and much more difficult to level off. In order to level off at 50 feet below surface, the diving officer must begin to turn the nose upward before that depth is reached. The length of the submarine makes this maneuver difficult if the angle of the dive is steep.

Since modern submarines are close to 300 feet in length, it is easy to understand that the shallow dive is preferred.

Even with a shallow dive the time for a submarine to get under water is exceedingly short. Submerging completely in a minute or less is a common occurrence.

One foreign navy claims that its 280 foot ship can submerge in less than 30 seconds. This is a great improvement over the first Holland boats that took about twenty minutes to submerge on their trials. Later, after much practice, the Holland boats submerged in about three minutes.

Because the submarine depends on speed and surprise for both offense and defense, rapid submerging and surfacing are of utmost importance. The submarine is not a heavily armored boat and one shot through the pressure hull may be fatal. The captain must always be prepared for a quick dive and the crew must always be on the alert to execute it properly.

   
IN DIVING, THE SUPERSTRUCTURE FLOODS THROUGH HOLES NEAR CONNING TOWER. ON SURFACING, IT DRAINS THROUGH THESE SAME HOLES. Official U. S. Navy Photograph.

ELECTRIC POWER AND COMPRESSED AIR

AS you have seen, the Diesels have become the basic source of power on board a submarine. As the submarine has developed, so have the Diesels. In modern submarines a Diesel installation will produce 6,000 H.P. or more. Furthermore, the newer models take up less space, are lighter in weight, and more efficient. They are easier to maintain.

Until recently the Diesel engines were connected directly to the propeller shaft. Two intermediate clutches were installed so that the Diesels could be disconnected from the propellers and the motors. These were needed to start the submarine and to charge the batteries. In an emergency both the motors and the Diesels can be connected to the propellers to give added speed.

Recently Diesel-electric drives have been substituted for the direct drive Diesels. Now the Diesels do not connect to the propellers at all, but run generators manufacturing an electric current. This electric current is sent through cables to motors attached to the propeller shaft. The motors turn the propellers.

It may not seem logical to change the Diesel power into electricity and then use this electricity to turn the propellers, when the Diesels could do the job directly. But there are certain advantages to be gained from the use of a Diesel-electric drive that make this more complex arrangement worth installing.

Even though more machinery is involved, a saving of space is affected because it is no longer necessary to have a long direct shaft from the Diesels to the propellers. The engine room, for both safety and convenience, may be divided into two compartments instead of a single large one. In one compartment the Diesels and the generators manufacture electricity.

The cables carrying this current may go alongside the hull to a second compartment, which houses the motors, propeller shaft, switchboards, etc. This means that the entire engine crew does not have to stay in the same compartment with the hot Diesels.

At the same time, operation is made easier and there is actually a better control over the power supply. The submarine is easier to reverse, steer and maneuver.

   
ENGINE ROOM. British Official Photograph—Crown Copyright Reserved.

While these points may not seem important, they are of real value. The space saving alone has made possible better living accommodations for the officers and crew. Maintenance work is made easier, even though there are more machines to be cared for.

While the Diesels remain the basic source of power, electricity has become increasingly important on submarines. The electricity generated by the Diesels is used directly and indirectly. When cruising on the surface much of the power is used directly.

Besides the main propulsion motors, electricity runs many other motors on board. Motors operate blowers needed for the circulation of air. The large rudder and hydroplanes are turned by electric motors. Motors also raise and lower the periscopes and operate many pumps. The motor that runs the gyroscope is small but very important.

Electricity, of course, furnishes power for the lights on the submarine including searchlights and interior illumination. All the cooking is done on electric stoves and oven. Without the electric current the radio would be useless and so would the oscillator and other devices.

When submerged, even more electricity is needed than when on surface. Since the Diesels must be cut off the instant the ship goes under, the electricity from the batteries on board not only propels the submarine but does all the other work as well. These batteries that store up energy and supply all the power when submerged are exactly the same type as those in automobiles.

An automobile battery contains three connected cells, mounted in a single case. Each cell is about eight inches square and three inches wide.

A single cell aboard a submarine is about five feet high and weighs over half a ton. Instead of three connected cells, the submarine may have 100 or more.

The immense size of the batteries may be more easily pictured if you know that those on the U. S. O-class submarines (our smallest ships) weigh 65 tons. On a modern ship they may weigh 100 tons or more and may cost over one quarter of a million dollars to install.

Except for these differences in size, the automobile battery and the submarine battery are identical. They are both batteries of the lead-acid type. Each cell produces about two volts of current. These batteries contain plates of lead and lead oxide arranged close to each other in a solution of sulphuric acid.

The battery may be recharged by sending an electric current into it from the Diesel-powered generator.

   
STARTING THE MAIN MOTORS IN ENGINE ROOM. COUNTING THE VALVES GIVES AN IDEA OF THE COMPLICATED CONTROLS. IF YOU DO NOT FIND 35 VALVES, TRY AGAIN. British Official Photograph—Crown Copyright Reserved.

The batteries must be charged regularly and tested continually. Automobile drivers are urged to check their batteries every week and give them the care they need. Very few drivers are conscientious enough to do this.

On a submarine constant attention to the batteries is part of the daily routine. These batteries are too valuable, too important, and too expensive to receive anything but the best of care. Recharging is done under carefully controlled conditions, so as not to damage the battery plates by subjecting them to excess current.

The specific gravity is checked at half-hour intervals during the eight or nine hours it takes to recharge a completely discharged battery. As the batteries become fully charged, the charging rate is altered until it is greatly reduced. The temperature of the batteries is also observed. If the charging rate causes the batteries to become warm it must be slowed down.

Since the Diesels must furnish power for charging the batteries, this can only be done when the boat is on the surface. In wartime there may be real difficulties. While in enemy waters a submarine may have to remain submerged all during the day.

At night if conditions are favorable it may rise and charge the batteries. Should the presence of enemy ships prevent this, the captain may have to curtail his undersea operations till he can get his batteries charged.

In the process of charging the batteries, hydrogen gas is normally given off. If batteries are charged too rapidly, an excess of hydrogen gas will form. This is injurious to the batteries.

Also, hydrogen gas is a serious hazard aboard a submarine. Three or four per cent hydrogen gas mixed with air forms an explosive mixture that might easily be ignited by sparks from the electrical equipment. For this reason, the battery compartments have their own ventilating system. Thus the air is frequently changed and the hydrogen does not reach a dangerous concentration.

In addition a hydrogen indicator is placed in the battery compartments. This measures the hydrogen in the air and warns the captain when the concentration of hydrogen approaches the danger point.

   
THE CAPTAIN MUST ENSURE QUALITY AIR FOR HIS CREW. British Official Photograph—Crown Copyright Reserved.

Compressed air is also used as a source of power on the submarine. It has more limited application than electricity, but it is admirably suited for driving water out of the ballast tanks and for launching torpedoes. If the air supply fails, there are other pumps which will empty the ballast tanks, but the use of compressed air is fastest and most efficient for this purpose.

Compressed air is carried aboard in seamless bottles or flasks, under a pressure of 2,500 lbs. per square inch. The normal air pressure is 15 lbs. per square inch. Under this high pressure the bottles contain over 150 times as much air as at normal pressure. This enables a large quantity of air to be stored in limited space.

When the air is used and the pressure drops, a compressor may be started. Soon the pressure is brought back to normal. The compressor is only used to replenish the tanks when the submarine is on the surface. It may be used to reduce high pressures at any time.

The air compressor, like the Diesel engine, has pistons and cylinders. These do not make power. They use it. An electric motor moves the pistons up and down in the cylinders. On the down stroke a valve opens and air is drawn in. The valve shuts. On the up stroke the air is compressed and forced through a second valve into a tank or pipe line. Then the strokes are repeated.

The air is not compressed enough in one cylinder of the compressor. It passes into a second cylinder which compresses it more—then to a third cylinder, and finally a fourth. The second, third, and fourth cylinders are each smaller than the other and more heavily built.

Compressing the air heats it and makes the air expand. This makes the compressor less efficient. To overcome this difficulty, water jackets surround each cylinder, cooling the air as it is compressed.

Since the air pressure in the tanks is so high it cannot be safely used without very heavy piping. The pressure is lowered by a reducing valve to less than half before it is sent to all parts of the submarine. Air lines connect to the torpedo tubes, main and variable ballast tanks, and a number of other places where compressed air has to be used.

In use, the compressed air is controlled by valves similar to those on water pipes, but often larger and sturdier. Each member of the crew on duty is assigned to the operation of one or more valves. Normally valves in the central operating compartment will control the air supply to most of the ship, but duplicate valves are found at every piece of equipment using compressed air.

If any compartment is cut off, the air supply may be controlled locally. In addition to being a source of power, the compressed air in the bottles may be used as a reserve air supply for the men if it is necessary to stay submerged for an unusually long period.

   
British Official Photograph—Crown Copyright Reserved.

FRESH AIR

VENTILATION, whether it is in a house or aboard a submarine, involves seven distinct conditions. The sum total of these makes for a good air supply. Neglect of any one of the factors may seriously impair a system of ventilation. These factors are:
1. A continual supply of oxygen.
2. Elimination of excess carbon dioxide.
3. Freedom from odors.
4. Temperature within a normal range.
5. Humidity of proper degree.
6. Adequate air movement or circulation.
7. Elimination of dust, poisonous gases, etc.

Each of these is a factor in the fresh air supply of a submarine. Their importance depends largely on whether the ship is afloat or submerged, and on the prevailing climatic conditions.

For a submarine cruising on the surface with air valves and hatches open, the maintenance of the oxygen supply need not be considered. Plenty of fresh air will be sucked in by the blowers. This air contains slightly more than 20% oxygen and it enters the submarine in sufficient amounts to meet the needs of the crew and the Diesels, which use large amounts of oxygen in combustion.

Under these conditions the elimination of carbon dioxide also need not cause Concern, as the exhaust valves adequately remove air from the submarine, once it has circulated.

Odors may be present when the ship is on the surface, but these will depend in part on the temperature, humidity, and circulation. Odors may be localized in the engine room or in the cook’s galley, but in both these places blowers remove the air rapidly and help keep odors at a minimum.

   
GOOD FOOD AND PLENTY OF IT IS IMPORTANT ON A SUBMARINE. Courtesy of U. S. Navy Recruiting Bureau.

There are no heating or cooling systems on some submarines. Air circulating in these ships is the same temperature as air on the surface, which may be hot or cold, varying with the latitude and the season.

Because of its shape and structure, the submarine is a difficult boat to ventilate, and the chances are that in hot weather the circulating air will not go far in keeping things cool. The submarine may become unbearably hot—so hot that it affects the crew in carrying on with their tasks.

But, as we say, “It isn’t the heat, it’s the humidity.” The air in the submarine is invariably humid. The close compartments do not permit a good circulation of air. Evaporation is retarded. The cold metal pipes and fixtures cause moisture to condense from the humid air, adding another source of discomfort and annoyance.

As a matter of fact, the humidity in submarines may even cause short circuits in the electrical wiring. The blowers help, of course, but if the weather is warm, the humid heat may be unbearable inside the submarine.

In all modern submarines electric blowers send fresh air through metal ducts to each compartment. There are also exhaust ducts which make the circulation of air complete. Until recently this circulation was far from perfect. Inadequate control sometimes brought blasts of cold air below and, at other times, failed to produce a comforting breeze.

The last factor in ventilation involves poisonous and dangerous gases. Both of these may occur in a submarine. Should sea water enter the batteries, a poisonous gas, chlorine, is generated. Even in small amounts this is dangerous for the crew.

When the batteries are charging, a dangerous explosive gas (hydrogen) is given off. To prevent the hydrogen from reaching a concentration, when explosions might occur, each battery compartment has its own ventilating system.

In the most recent submarines complete air-conditioning apparatus has been installed, so that all factors of ventilation are under continual control. This not only makes the submarine more livable, but actually increases the efficiency of the crew.

Except in these very latest ships, ventilation is never perfect. Odors, heat, and humidity may at times make the submarine almost unbearable to a visitor. Yet these conditions are more annoying than dangerous. The ventilation in all submarines is sufficient to maintain normal health.

   
WHEN CONDITIONS PERMIT, MEN COME ON DECK FOR A BREATH OF FRESH AIR. THE U.S.S. S-1. From Ewing Galloway.

Once the submarine has submerged, an entirely new set of ventilation problems prevails. The hatches are sealed and the intake valves closed. The ventilation of the submarine changes from an open system to a closed one. No longer is the tremendous supply of oxygen available. No longer can exhaust gases be turned loose to the wind.

Temperature, humidity, and circulation can only be regulated by moving air from one part of the submarine to another. In some types of submarines the air ducts pass outside of the pressure hull but beneath the superstructure. It is, therefore, possible to circulate the air through these ducts, once the submarine is submerged.

In this process air passes through pipes that are in contact with the ocean water and hence are cooled. This type of ventilation involves the opening of air valves that are a potential source of danger, should anything happen to them when the ship is under water.

To appreciate what problems are involved in a closed system of ventilation, we must first understand in detail the process of breathing.

Breathing is an automatic process produced by the movements of the diaphragm and muscles of the chest. These movements change the capacity of the chest cavity and automatically result in a movement of air in and out of the lungs. While the total capacity of the lungs is about four or five quarts, only about one pint of air is taken in during each average breath and not more than three or four quarts in the deepest breath that a person can take.

The usual rate of breathing is about 16 or 18 times a minute. The amount of air taken in during the course of a day is considerable—about 300 to 400 cubic feet.

Only about 20% of the inhaled air is oxygen. Because of the mixing of air in the lungs, not all of the oxygen is used up in each breath. Carbon dioxide, nitrogen, and water vapor are also taken in with the oxygen. The average percentage of these in inhaled and exhaled air is as follows:

   
Percentage of components of air, Oxygen, Carbon dioxide and Nitrogen present in inhaled air vs. exhaled air from the human lung.

Normal air contains about 1% water vapor; exhaled air about 6%.

Once these gases are within the lungs, temperature, pressure, and other conditions determine how much of the gas will actually pass into the blood stream. Carbon dioxide, for example, diffuses much faster than oxygen and it is less soluble in the blood fluids. For these reasons, carbon dioxide normally diffuses outwardly and oxygen diffuses inwardly.

A number of conditions affect the rate of breathing. Exercise is one condition. A man while working will consume 20, 30, or even 50 times as much oxygen as he will when resting. Blood will circulate through his body more rapidly. Breathing is faster and deeper.

The same effect is produced when the amount of carbon dioxide in the air increases. The carbon dioxide stimulates breathing. When more than 1/2 of 1% carbon dioxide is present in air, the rate of breathing is clearly and definitely increased. The amount of increase is shown in this table:

   
Percentage of Carbon dioxide in air vs. percentage increased breathing per minute.

Modern submarines are large enough to stay submerged for about a day without an appreciable effect on the air. The oxygen content will slowly decrease. Carbon dioxide content and humidity will increase. More body odors may be present, but while the air will be stuffy the crew will suffer no physical effects.

If it is necessary to stay submerged for an even longer period, steps can be taken to keep the content of the air above the minimum requirements. By means of a simple apparatus the captain can quickly determine the percentage of carbon dioxide in the air.

When this approaches 5%, soda lime may be spread on the floor of the submarine or beneath one of the blowers. As the air circulates over this chemical, the carbon dioxide is removed. Tables, which the captain has aboard, enable him to figure out how much oxygen is available for each crew member and how long it will last.

If the crew develops symptoms of oxygen deficiency, air may be released from the compressed air tanks to raise the oxygen content. Some submarines carry extra tanks of pure oxygen to be released in such an emergency.

Experimental studies conducted in scientific laboratories have shown that an individual can breathe in an atmosphere containing 25 to 50 times as much carbon dioxide as normal, without suffering ill effects.

In another experiment a man remained for several days in an air-tight chamber. During this time fresh air was added at the rate of only four cubic feet per minute—1/12 of the normal air requirements. These experiments indicate how well the human body can adjust itself to major changes in the composition of the air.

The submarine captain takes advantage of this knowledge if it is necessary to stay submerged for an extraordinary length of time. In such an emergency he will order the crew to lie quietly in their bunks—thus using less oxygen.

By the use of soda lime he will keep the carbon dioxide content down to a minimum; not because the carbon dioxide is dangerous, but because it stimulates breathing which, in turn, would use oxygen faster.

If it is necessary to use oxygen, he will add it gradually and before the men have become weakened by lack of oxygen. He knows that a sudden breath of pure oxygen may make a man dizzy, drunk, or nauseous.

As soon as the submarine is able to return to the surface, it will be well ventilated. The chances are that the crew will have suffered no ill effects, except for possible slight headaches.

   
British Official Photograph—Crown Copyright Reserved.

Under certain conditions it may become necessary for the crew of a submarine to breathe compressed air. This only happens in an emergency—as when the submarine is partly flooded or when air is used from the compressed air tanks. Normally the nitrogen taken in with each breath does not diffuse through the lungs and enter the blood in appreciable amounts.

Under pressure, conditions are altered. Nitrogen will enter the blood stream and will remain dissolved in the blood as long as the pressure is maintained. If the air pressure is not greater than 2 or 2 1/2 times normal—the equivalent of the pressure under 50 feet of water—the body will adjust to the change without serious inconvenience.

Should the members of the crew become subjected to air pressure greater than twice normal, great care must be taken, when possible, how the pressure is lowered to normal again. If the pressure is lowered too rapidly, the nitrogen that has entered the blood and the tissues will not have a chance to return to the lungs and diffuse out.

Instead, bubbles of nitrogen may form in the blood vessels, heart, brain, and joints. This produces most serious symptoms including cramps, nausea, unconsciousness, and paralysis.

Unless the pressure of these nitrogen bubbles can be quickly removed, serious injury or death may result. This condition is known as the bends,” or caisson disease. The bends may affect any man working under pressure: divers, tunnel workers, sandhogs, etc.

During rescue attempts in an emergency the avoidance of bends must be given serious attention.

Bends may be prevented by slowly returning the air pressure to normal, so that the body has time to get rid of the nitrogen.

If symptoms of bends do appear, the pressure must be raised again until the bubbles of nitrogen are reabsorbed. Then the pressure may be gradually lowered. Usually, this problem isn’t important on board a submarine because the air pressure is normal except during emergencies or disasters.

   
RECOMPRESSION CHAMBER. SAILORS MUST BE ABLE TO STAND FIFTY POUNDS PRESSURE IN THIS CHAMBER BEFORE THEY CAN ENTER THE SUBMARINE TRAINING SCHOOL. Official U. S. Navy Photograph.
   
THE DOUBLE DOORS ARE SEALED AND THE RECOMPRESSION CHAMBER IS IN USE. THE PRESSURE GAUGE IS HALF HIDDEN BY THE OFFICER’S ELBOW. Official U. S. Navy Photograph.
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