The Physics of War (31 page)

In World War II, active sonar was generally kept to a minimum, so most submarines relied heavily on passive sonar. But modern techniques and devices have improved active sonar, so both active and passive sonar are now used extensively. There are, of course, other problems with both types of sonar. The signal is influenced by the depth of the water and by the water's temperature and solubility, and these factors have to be taken into account. In addition, there is what is called a thermocline in the ocean. It's a sharp division between the warm
surface water and the cold, still waters below. As sound waves pass through it they tend to be deflected, and this has to be taken into account as well.

Sonar is used not just by submarines. Objects called
sonobuoys were used extensively during World War II, and they are still used. Sonobuoys are small systems, about three feet long and five inches across, which can be easily dropped or ejected from an airplane or ship. They float in the water and can be either active or passive. Their signal is picked up by a nearby ship or an airplane. They do have limitations, however. They have a limited lifetime (depending on their batteries) and a limited range, but they have proven to be useful.

TORPEDOES

Robert Fulton is believed to have been the first to equip a submarine with a torpedo. His submarine, the
Nautilus
, was equipped with a torpedo that was actually little more than a box of dynamite designed to explode beneath enemy ships. He used it in a demonstration in France in 1801 to sink a small ship, and again in a demonstration in England, but he didn't manage to get much interest from either government.
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Torpedoes first came into their own during the American Civil War, and they were used most effectively by the Confederate navy. At that time they were mounted on a boom or spar in the front of the submarine, from which they were attached to an enemy vessel. Sometimes they were detonated by the blow they received when they struck the ship, and sometimes timing devices were used. Free-floating torpedoes, or what we today would call mines, were also used. Twenty-two Union ships were sunk by Confederate torpedoes, while only six Confederate ships were destroyed by Union torpedoes. One of the most famous sinkings was achieved by the Confederate submarine
H. L. Hunley
. On the night of February 17, 1864, it rammed and sank the Union ship USS
Housatonic
, but the explosion was so great that it damaged the
Hunley
, and it also sank with all men aboard. In 2004 the remains of the
Hunley
were located and raised.

One of the most significant advances in torpedo technology came in 1864. An Englishman, Robert Whitehead, who was working in Austria, became interested in the torpedo and decided to build a model that would run just under the surface of the water. In October 1866, he had his model ready. It was driven by a two-cylinder compressed-air engine, had a top speed of about seven and a half miles per hour, and a range of approximately two hundred yards. Officials in Austria were so impressed that they immediately purchased it. He did, however, also sell the rights to manufacture it to several other countries. Strangely, the US Navy was not interested in it.

HOW TORPEDOES WORK

A modern torpedo is a self-propelled projectile. It is stored in the launching area until it is fired. When fired, it is given an initial velocity, but as it moves out into the water several other forces act on it. Gravity pulls it downward, and the drag of water on it creates a friction that slows it down. The friction created by the drag of water is, indeed, quite large—about a thousand times greater than the drag created by air. Depending on design, there is another force that also comes into play, namely the buoyancy of the torpedo itself. All of these forces have to be taken into consideration.

The earliest torpedoes used compressed air to turn their propellers. Within a few years, however, it was found that compressed oxygen was more efficient, but oxygen systems posed a danger to submarines when they came under attack. Because of this, the Germans used a small electric motor powered by batteries. It had an additional advantage in that bubbles were not released as a torpedo moved toward its target. It was slower and had a more limited range than previous torpedoes, but it was much cheaper to build. The United States also soon introduced an electric motor model called the Mark 18.

Torpedoes can be aimed at a target and fired in the same way that an artillery shell is fired. In this case, there is no control over the torpedo once it leaves the submarine, and no changes can be made if the target sees it and tries to outmaneuver it. Because of this, guided torpedoes are frequently used. In some cases they are guided to the target by its sound or by the use of sonar. They are referred to as acoustic torpedoes. The first acoustic torpedoes were employed late in World War II by the Germans, and they proved to be quite effective against both surface ships and other submarines.

Acoustic torpedoes are equipped with acoustic sensors and transmitters in their nose. They are therefore able both to detect sound coming from the target and to produce sonar reflections. Usually the torpedo starts by using passive sonar. Once the passive sonar has detected the enemy, it switches over to active sonar, which allows it to send out a sound beam to locate the enemy more exactly. It then attacks.

Another effect that is useful in the case of torpedoes is what is called supercavitation. When an object moves through water at high speed, the pressure behind the object is lowered, and, as a result, a bubble is formed that can encompass the object. This is particularly useful in the case of a torpedo because water creates a large frictional drag on it. If the object is in such a bubble, however, the drag is significantly reduced. Torpedoes are therefore designed to produce supercavitation bubbles.

SUBMARINES IN WORLD WAR II

Submarines were used extensively in World War II by both sides. They were particularly effective for the Germans at the beginning of the war and for the Americans against the Japanese toward the end of the war. Although they were limited in speed, range, and endurance while they were underwater, they could attack with total surprise and inflict devastating damage, so they were highly lethal. Although early submarines were basically underwater crafts, they spent a lot of time on the surface, submerging only when they were engaged with the enemy.
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The Treaty of Versailles that ended World War I did not allow Germany to build either surface ships or submarines. But the Germans soon found that they could build submarines much more quickly and with more secrecy, so they concentrated on them, and by the beginning of World War II they had the largest fleet of submarines in the world. Furthermore, they had also now developed several new technologies and techniques, so their submarines were better than the British and American ones. The early U-boat success of the Germans was mainly due to a World War I U-boat captain
Karl Doenitz. He built up the submarine fleet and equipped it with highly trained crews, and he developed what was called the
Wolfpack tactic, which was particularly effective. To initiate the tactic, German U-boats would spread out across a large section of the ocean looking for convoys. When one was located, the captain of the U-boat that located it would signal the other U-boats, and they would group themselves around and ahead of the convoy. All convoys were escorted and protected by destroyers and other battleships at that time, so the U-boat captains had to outsmart the escorts. They would therefore attack together at night, creating as much chaos as possible; this would give the German submarines a much better chance of escaping. Allied losses were high when this tactic was first used.

The main objective of German U-boats was to cut off supplies to Britain from the United States. And the U-boats sank so many merchant ships that it appeared they might achieve their objective. There was a problem, however: members of the German high command, and Hitler in particular, didn't realize how effective their submarines were. Hitler was concentrating on the land war, and submarines were not high on his list of priorities. So when Doenitz asked for more U-boats, Hitler turned him down.

Eventually the British and Americans developed very effective antisubmarine devices and techniques. And by 1943 the Wolfpack tactic was losing its effectiveness. Radar and sonar were being used along with a particularly useful surface technique called Huff Duff, in which radio sources were pinned down
by triangulation. In addition, British code experts finally broke the code the German U-boat captains were using, and, as a result, they knew when and where to expect an attack. In May 1943, Doenitz lost forty-one U-boats in three weeks, and the tide began to turn. Until the end of 1942 the Germans had been sinking fourteen ships for every submarine loss, and now they were losing their submarine fleet at a crippling rate.

U-boats still had to come to the surface to recharge their batteries, and they were particularly vulnerable above water now. They could easily be located by radar and Huff Duff, and airplanes would be quickly dispatched to attack them. As a result, they were forced to stay submerged most of the time. The Germans eventually developed a snorkel so that they could recharge their batteries while just under the surface, and this helped. But in the end, Germany lost almost 80 percent of its U-boats. In addition, British submarines began sinking German submarines at a high rate; in all, they sank thirty-nine.

Submarines were also used effectively in the Pacific Ocean by the Americans against the Japanese. America entered the war following the surprise attack on Pearl Harbor by the Japanese. In two hours, Japanese pilots killed two thousand four hundred people and wounded another seven hundred. And although they crippled the US fleet, they ignored the nearby submarine base and the fuel and ammunition supply depots. In addition, all the large US aircraft carriers were at sea during the attack. For this reason, the main American fighting force that was left consisted of aircraft carriers and submarines. Unfortunately, neither the submarines nor the torpedoes they carried were a match for the Japanese and German submarines.

At the beginning of the war the American submarines had no radar, and they were armed with relatively poor torpedoes that frequently misfired. Nevertheless, they fought back quickly with what they had. One month after the attack on Pearl Harbor the USS
Pollock
sank a Japanese freighter near Tokyo Bay. And relatively early in the war the United States made an important breakthrough: cryptanalysis groups deciphered Japanese coded messages. So they knew what the Japanese were planning—their strategies and movements. And this, of course, proved to be extremely helpful.

Although the American submarines were inferior at the beginning of the war, a tremendous effort went into improving them, and by August 1942, the first radar systems were installed in US submarines. Then new Gato-class submarines began replacing the older submarines. After many embarrassing experiences with their torpedoes, they were also gradually perfected, and new tactics were developed. In 1943 they even started copying the German Wolfpack tactic, but it didn't work as well against the Japanese.

Although the Japanese submarines and torpedoes were superior at the beginning of the war, the Japanese never took advantage of it. They used their submarines mostly against American warships, which were much more difficult targets than merchant ships. And they were generally used in connection with groups of warships.

By the end of 1943, American submarines were beginning to inflict a tremendous amount of damage to Japanese naval forces. Although the submarine fleet constituted only 2 percent of the overall American navy, it destroyed 30 percent of the Japanese navy, including eight aircraft carriers, a battleship, and eleven cruisers. It also destroyed 60 percent of the Japanese merchant fleet, which created a real problem for Japan. It quickly began to run out of resources.

Submarines were particularly effective in the Battle of the Philippine Sea in June 1944, when they sank two of the largest carriers in the Japanese fleet. Shortly after 8:00 a.m. on July 19 the USS
Albacore
sighted the
Taiho
, the largest and newest carrier in the Japanese fleet. As the captain of the
Albacore
started to fire torpedoes, however, its torpedo data computer failed, and the torpedoes had to be fired manually by aiming them as accurately as possible. Six torpedoes were fired; four of them missed and a Japanese pilot spotted one and crash-landed his plane into it before it reached the carrier. But the last one got through, striking the carrier on the starboard side, rupturing two of its aviation fuel tanks. At first the damage did not appear to be serious, but it produced a lot of explosive fumes. And an inexperienced damage-control officer ordered that the ventilation system be turned on full blast to clear out the fumes, but this only spread them, increasing the danger of ignition. Hours after the initial torpedo impact, several large blasts occurred. Before long the carrier was underwater.

A few hours later the submarine USS
Cavalla
sighted the carrier
Shokaku
. It fired six torpedoes at it, hitting it with three. One of the three hit its forward aviation tanks, causing them to explode. Soon there were other explosions, and within minutes the entire carrier was in flames, and it quickly rolled over and slipped beneath the waves.
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This battle was one of the last for the Japanese navy; it was never able to recover from the serious losses it incurred.

After World War II, a new and vastly improved submarine came into use, the nuclear submarine, which we will discuss in a later chapter.

World War II was the deadliest and most destructive war in the history of the world. A large number of nations—fifty in all—took part in it. And no previous war had such a profound effect on physics and science in general. A large number of weapons were developed and improved over the six years of the war, and a number of important new innovations came about as a result of physics:

• Advanced techniques in radar.
  
• Rockets, including the V-1 and the V-2.
  
• The first jet airplanes.
  
• Code-breaking computers and other computer developments, including ULTRA, ENIAC, and COLOSSUS.
  
• Proximity fuses and many other guided-artillery devices.
  

Physics and other sciences were mobilized on a large scale during World War II, with large research and development labs directed mainly at war projects coming into being for the first time. Some of the larger ones were the radiation lab at MIT, Bletchley Park in England, the Los Alamos lab, and the Manhattan Project, and of course the Germans also had their research labs.

Physics became critical in relation to accuracy of artillery weapons, strategic bombing, navigation of airplanes, ships, and submarines, and the development of radar, to mention only a few. It was the first “high-tech” war, and it was largely fought using new technologies, many of which came from physics.

HOW THE WAR STARTED

Historians generally agree that World War II was primarily a result of the surrender conditions that were imposed on Germany at the end of World War I. But it was also due to the economic conditions that soon came about after the war. Unemployment was high throughout Germany, and inflation made German money almost worthless. Exacerbating this was the worldwide depression that hit in 1930. Trade fell off and millions of workers throughout the world lost their jobs. The economic situation was particularly bad in Europe, and people began to look to their leaders for change. They wanted relief.
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During this time several dictators came to power. Mussolini and his Fascist Party took over Italy in 1922, and in the early 1930s the Nazi Party under Hitler began to rise in Germany. In addition, military leaders began to control Japan. As a result, all these countries came under the control of totalitarian governments that did not allow any opposition. Furthermore, these leaders promised great things; they assured their people that the nation would be great again and that there would be a significant turnaround. And the people believed them.

Soon after he gained almost complete control, Hitler was already thinking of retaliation against France, England, and other nations. He was bitter, and he had many bitter followers. He was hindered by the Treaty of Versailles, which prohibited Germany from organizing a large army or rearming in any significant way. But Hitler wasn't interested in complying with it, and he soon entered into a coalition with Russia. This arrangement allowed him to manufacture military weapons deep in Russia, away from the prying eyes of inspectors. In return, he gave Russia many military secrets for new technical devices. Not only were German tanks and airplanes being built deep in Russia, but training camps were also set up to train pilots and develop a new, highly skilled army. Much of the manufacturing was done by the giant German steel company Krupp. Finally, by about 1935, Hitler gave up all secrecy and began manufacturing directly in Germany. He almost dared England and France to try to stop him.
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During this time England and France were also mired in the depression, and they were directing very few resources to the military. It was a cooling-off period for them, but they were becoming worried about Germany.

READY FOR WAR

By the late 1930s Germany had rebuilt itself into a major military power, unmatched by any other country in Europe. Airpower was a major concern to
Hitler. World War I had been fought mainly in the trenches, and for several years it had been a stalemate, with neither side making significant advances. Hitler was determined to overcome this; he didn't want a repeat of World War I. New techniques and strategies were therefore needed, and one of the main parts of his new strategy was a large and highly efficient air force (the Luftwaffe). And by the late 1930s Germany had an air force unmatched in Europe. Not only were German planes superior to those of both England and France, but Germany also had a much larger number of planes: 5,638 fighters and bombers against 1,070 for the English and 1,562 for the French. In addition, the pilots in England and France had grown rusty, but German pilots were highly trained and had seen action in the Spanish Civil War between 1936 and 1939. Furthermore, Germany had a large number of long-range bombers that were a significant threat to England.

The German tanks were no better than the French tanks, but the Germans had many more of them, and all of them were equipped with radios. And they had beefed them up so that there was little defense against them. Antitank weapons existed, but there were so few of them available that they would be of little help. Most of the opposing bullets bounced off the tanks and did little to stop them. Germany's biggest advantage at the time was a new strategy called
blitzkrieg
(German for “lightning war”). It was based on fast movement using a concentrated tank and airplane attack along with fast-moving troops. The idea was to continue the attack regardless of the opposition; in short, stop at nothing. And it worked well. German tanks were relatively fast and almost impervious to artillery, and they were accompanied by an all-out air attack, mostly by dive-bombing Stukas. The Stuka was quite effective during the early part of the war; it delivered its bombs as it dove down toward its target, and because of this it was highly accurate.

Hitler began by attacking Austria. He had always seen Austria as part of Germany, as he had been born in Austria, and he wanted to annex it. But the Treaty of Versailles forbade a union between the two countries. Nevertheless, he invaded Austria in March 1938, and to his delight there was little opposition. Large crowds actually cheered him as he entered in triumph. Austria became part of the German Reich. Next came Czechoslovakia, beginning with the annexation of the northern and western border regions. These regions contained many Germans, and Hitler's pretext for occupation was that he was freeing them from suffering under the Czech government. In March 1939, Hitler moved his troops into the remaining parts of Czechoslovakia, which was now weak and almost powerless to resist. Although the Czechs fought bravely, they were no match for the Germans and were quickly overcome.

Hitler then looked toward Poland, but there were several problems. Poland had an agreement with France and England, and he had no excuse for an invasion. Poland had been arming itself for such an invasion, but it was no match for the German military in numbers or in tanks or airplanes. Furthermore, just prior to the invasion, Hitler had signed a pact with the Soviets. They agreed to remain neutral if France and England entered into the war. In return, Hitler agreed to share Poland with the Soviets after it was conquered.

The attack began with several events staged by the Germans to use as an excuse for the invasion. During the night of August 31, the Germans staged a fake attack on a radio station near the border, using Germans posing as Polish troops. The next morning Hitler ordered an attack on Poland without a declaration of war. The German Luftwaffe attacked the Polish town of Wieluń, killing close to twelve hundred people, mostly civilians, and leveling about 75 percent of the city. Within a short time German troops attacked the western, southern, and northern borders, as the Luftwaffe began bombing major Polish cities. Their blitzkrieg tactic was used effectively in the attack. Polish forces were quickly forced back from their positions near the border as the Luftwaffe bombed Polish airstrips and many early warning sites.

Within two days of the initial attack, France and England declared war on Germany. The Poles hoped they would soon get aid, but very little came. Polish forces managed to hold off the Germans for two weeks, but then the Soviets invaded Eastern Poland on September 17. The Poles now had to fight on two fronts, and they could do little to stop the two advancing armies. By October 6, German and Soviet forces controlled most of the country. Surprisingly, though, the Poles never formally surrendered. They soon organized an extensive underground force that continued to fight the Germans for years.

THE BATTLE OF FRANCE, AND DUNKIRK

After the Polish invasion, Britain deployed troops to the continent, mainly France, but little happened. Neither side attacked, and for several months both sides waited. It was later referred to as the “phony war” by the British and the “sitting war” by the Germans. Then, in April 1940, Germany invaded Denmark and Norway. Denmark succumbed almost immediately and Norway was overcome in about two weeks. Still, England and France did nothing. Then Winston Churchill became prime minister of England.
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On May 10, 1940, the stalemate was broken when the Germans invaded France, Belgium, the Netherlands, and Luxembourg. Employing the blitzkrieg
tactic that they had used earlier, they overran the Netherlands in a few days and Belgium in a few weeks. The French, however, were a more significant foe, and they also had help from a relatively large British force, so it was expected that they would stop the German attack, but they didn't. The German army quickly burst through the Ardennes and moved rapidly to the west before turning northward toward the English Channel, reaching it on May 20. The German spearhead separated the British and French forces, backing them up against the sea. It appeared that the Germans might trap and capture them. But surprisingly, the Germans stopped their advance at this point for about three days to regroup and plan their next move. This gave the Allies time to prepare for an evacuation across the English Channel. There were far too many soldiers for the ships available, but soon after news of the situation reached the English public, a large flotilla of merchant ships, fishing boats, pleasure boats, and other craft raced across the channel to the beach at Dunkirk. And over the next nine days, 380,226 English and French soldiers were rescued and brought back to England. They were attacked from the air by German planes as they boarded, but the loading continued. Finally, they had to evacuate under the cover of darkness, but the vast majority of the stranded soldiers made it out safely. Two French divisions remained behind to protect the evacuation, and although they slowed the German advance, they were eventually overcome and captured. The remaining French army surrendered on June 3, and the Germans marched into Paris on June 14. The formal surrender was on June 22.

THE RADAR ADVANTAGE

Both sides had developed radar by the outbreak of World War II, but the British took advantage of it to a much greater degree. They developed it extensively during the early part of the war, and they used it much more effectively than the Germans. The Germans, in fact, underestimated its possibilities and never took it seriously. But they found it to be a serious problem when they attacked England, and indeed it played a large role in the British victory in the Battle of Britain.
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When researchers started working on the new technique, the term
radar
was not yet in use. The technology was referred to as RDF, meaning range and direction finding. The earliest research was initiated in 1935 by the British Aeronautical Research Committee, which was headed by Henry Tizard. By this time Germany was making no secret of its military buildup, and many in Britain were beginning to get worried. A research project for detecting incoming planes—particularly German bombers—was initiated by Robert Watson-Watt. His team soon showed
that a plane could be detected at a distance of seventeen miles using reflected radio beams. And soon an extensive RDF program was in full swing.
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In 1936 the program was moved to Bawdsey Research Station in Suffolk, with Watson-Watt as its director. With a team of many of the best scientists and engineers in England, Watson-Watt improved the technology significantly. And within a short time, a chain of radio stations was constructed along the south and east coasts of England. It was referred to as the Chain Home, or CH system. It was relatively simple, and because it used radio waves from ten to fifteen meters long (20 to 30 MHz), the images that were received were rather fuzzy. And at the time, oscilloscopes were used to display the images. It was crude, but with a little work the operator could determine the direction and approximate altitude of an incoming bomber.

Using this system, British operators could “see” incoming German bombers and send fighter planes out to encounter them. It was particularly helpful in that these planes could be dispatched only when they were needed so that they didn't have to waste a lot of fuel patrolling the English Channel.
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It didn't take long for the Germans to realize that the British were detecting their airplanes, so early on they tried to bomb some of the visible radio towers, but they were not very successful. Even when they disabled a particular system, it was usually back in service within a few days. As a result, they soon shifted to a new tactic. They decided to fly at very low levels, under the line of sight of the CH stations, but the British had another system called the Chain Home Low (CHL) system, which had originally been developed for another purpose (naval guns), and it was able to detect the incoming German aircraft.