The Physics of War (34 page)

In flight a rocket can tumble around one or more of three different axes, referred to as the roll, pitch, and yaw axes. Spin around the roll axis is no problem, but we want to avoid tumbling around either of the other axes. Gyroscopes are used for this, and also to assist in guidance. The vanes on the lower end of the rocket also help stabilize it.

The V-2 was to be Hitler's vengeance weapon, and in early September 1944 he declared that V-2 attacks would begin, and London was to be a major target. Over the next few months over fourteen hundred were directed at London. But their accuracy was poor and they were unable to hit vital targets. For the most part, the V-2 was a terror weapon, and it did, indeed, create a lot of terror as it shot across the English sky. Because of the speed of V-2 rockets (approximately 2,200 miles per hour) and their high-altitude flight, they were almost impossible to shoot down. In all, about 2,550 civilians were killed in London by V-2s, and another 6,500 were injured.

The Germans also built another, similar weapon called the V-1 “buzz bomb.” It was smaller than the V-2, with a length of twenty-seven feet, compared with the V-2's forty-six feet, and it was much slower. A pulsed jet engine powered it; air entered the intake of the engine where it was mixed with fuel and ignited by spark plugs. Shutters opened and closed at the rear of the device about fifty times per second, giving it the buzzing sound that inspired its nickname.

The V-1 was developed at Peenemünde at the same time that the V-2 was being built. It was not a ballistic rocket; rather, it was launched from ground sites using a ramp and catapult. It is therefore referred to as a cruise missile. The first V-1 attack took place in mid-June 1944, just before the V-2 attacks began, and the V-1 attacks were also directed toward London. Like the V-2, the V-1 could not attack specific targets, so it, too, was mainly meant as a terror weapon. But unlike the V-2, there was considerable defense against it. Some of the faster airplanes could knock it down in flight, and it was quite vulnerable to coastal artillery. In fact, by late August 1944, almost 70 percent of incoming V-1s were being destroyed by coastal artillery. In all, about ten thousand V-1s were fired at England. About 2,420 reached London, killing approximately 6,180 people and injuring 17,780.

OTHER WEAPONS AND SMALL ARMS

Tanks played a large role in World War II. During the German blitzkrieg, in fact, they seemed to be unstoppable, and the Allies were soon looking for weapons that could counter them. Over the next few years several types of warheads were developed that were able to penetrate the armor of a tank, and they employed an important physics principle. They were based on the idea of a shaped charge. A shaped charge is an explosion that has a shape that focuses the energy of the shell. It is based on what is called the Munroe effect, discovered by the American chemist Charles Munroe. Munroe showed that a hollowed end on a charge produces a much more powerful wave that concentrates the explosion along the axis of the charge. This is because the shock waves from the explosion are reinforced in this case.

When applied to stopping tanks, the warheads are referred to as HEAT warheads (high- explosive, anti-tank warheads). They create a high-velocity stream of metal that can push through relatively heavy tank armor. This stream actually moves at nearly twenty-five times the speed of sound. HEAT warheads are less effective if they spin, so they usually are fin-stabilized.

HEAT rounds caused a significant change in tank warfare when they were first introduced late in the war. A single soldier could now destroy a tank using a hand-held weapon. The search was soon underway for a protection from the new shells, and the Germans began protecting their tanks with armored or mesh skirts, which caused the HEAT shells to detonate prematurely.

Another type of shell was also used quite effectively against tanks. It was called the HESH warhead (high-explosive squashed head). It was originally developed for penetrating concrete buildings, but it was also found to be effective against tanks. In this case the explosive material is “squashed” when it hits the target so that it spreads out over a large area. A detonating fuse triggers it at this point, creating a larger shockwave due to its larger area. This shockwave moves through the metal to the interior of the tank, causing pieces of metal to fly off the interior wall at high speed. These metal pieces could injure or kill the crew and ignite ammunition or fuel inside the tank.

Both HESH and HEAT warheads were delivered against armored vehicles using bazookas. A bazooka is a rocket-powered, recoilless weapon originally developed by Robert Goddard while he was working on rocket propulsion. He and a coworker Clarence Hickman developed and demonstrated it to the US Army at the Aberdeen Proving Ground in Maryland in November 1918. At this point, however, it didn't use a shaped charge. It was teamed up with shaped charges in 1942, and it was first used in North Africa and by the Russians on
the Eastern front at about the same time. The early models were not too reliable, however, and some of them were captured by the Germans. The Germans quickly copied and improved on the early bazookas, and much to the surprise of the Allies, the German bazookas were more powerful than theirs and had greater armor penetration.

Another important development in which physics was involved was the proximity fuse. At the beginning of the war detonation of a warhead occurred when it hit the target, or after a certain time set on a timer. Both of these had disadvantages, and the full effect of most exploding shells was not realized. With the proximity fuse, the device detonates automatically when the distance between the target and the projectile is smaller than some predetermined value. Shells could therefore be made to detonate before they hit the ground—in particular, over the heads of enemy troops—which improved their effectiveness.

The fuse was based on electromagnetic principles; it contained an oscillator connected to an antenna that functioned as both the transmitter and receiver. As the shell closed in on the target it could determine how far it was away by analyzing the reflected signal. It was used quite effectively against V-1 buzz bomb attacks on England as well as during the Battle of the Bulge. It was also helpful in the defense against Japanese kamikaze attacks in the Pacific.

Radio-guided missiles were also used for the first time in World War II. The Germans developed an antiship guided bomb called the Fritz X. It was delivered by aircraft and was radio-controlled from the delivering plane. Signals were picked up by a receiver in the missile. Fritz X was not considered to be very successful, however. Similar guided bombs were also developed in England. Called GB-1s, they were dropped on Cologne, Germany. Another German guided bomb was the Kraus X-1; several Allied warships were heavily damaged by it. And the V-1 and V-2 were also radio guided.

Another of the ingenious devices to come out of the war was the Norden bombsight.
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One of the major problems during the early part of the war was accurate bombing from high altitudes. In 1943 a plane dropping a bomb from a high altitude had a CEP (circular error probability) of twelve hundred feet, which made the likelihood of hitting a target extremely low. It was so low, in fact, that both the air force and the navy had given up on pinpoint bombing attacks. Over several years, however, Carl Norden, a Dutch engineer who had immigrated to the United States, had been working on a bombsight. One of the main problems in using bombsights was leveling the aircraft so that the sight could be pointed straight down. Wind was also a serious problem. Norden's bombsight allowed bombs to be dropped at exactly the right time for hitting a given target. It used an analog computer consisting of gyros, motors, gears, mirrors, levels, and a
telescope. The bombardier would program the airspeed, wind speed, direction, and altitude into the device. The computer would then calculate the trajectory needed for the bomb to hit the target. Then, as the plane approached the target, the pilot would turn the plane over to autopilot so that it would fly to the precise point needed for the drop. It is said that with this device a bomb could be placed within a one-hundred-foot circle from a height of four miles.

The Norden bombsight was one of the major secrets of the war, and its existence was carefully guarded for the duration of the war. It was particularly effective in the bombing of Germany during the later parts of the war.

Finally, let's look at the small arms and infantry weapons that were used during the war. They were much more powerful, accurate, and lethal than those used in World War I. At the beginning of the war, however, some of the same weapons were used. The bolt-action rifles used in World War I were also used at the beginning of World War II. Later on they were used as sniper rifles, mostly because of their long range and high accuracy. A bolt-action rifle equipped with a telescopic sight was an excellent sniper weapon, but for close-up fighting soldiers needed a much faster rate of fire, and because of this, semiautomatic rifles were soon developed. One of the best American semiautomatics was the M1 Garand, and it soon became the standard American rifle of the war.

The submachine gun also played a large role in the war. It was the small, relatively light equivalent of the regular machine gun. Its ammunition, however, was much smaller and lighter, and this meant that it had a relatively short range, and its accuracy was not as high. But it was quite effective in short-range combat. The Germans used it extensively; their best-known submachine gun was the MP-18. The American equivalent was the Thompson submachine gun.

The major problem with the submachine gun was its inaccuracy and short range. In most battlefield situations soldiers needed both rapid fire and accuracy at a distance. The accuracy did not need to be as great as that of a standard bolt-action rifle, such as the Lee-Enfield or the Springfield, but a range greater than that of the submachine gun was desired. Because of this, the assault rifle was developed. It was first used by the German army; their MP-43 came into service in 1943 and was clearly a superior weapon. The American M-16 and Russian AK-47, which came into being after the war, were based on it.

Basic machine guns were still used, as they were in World War I, but they were now much lighter so that they could be handled by a single soldier. In most cases, however, a second soldier was needed for carrying ammunition and to help set it up and feed it during firing. Finally, other weapons such as hand grenades, flamethrowers, and light mortars of various types were also used. And most were more lethal because of technical advances.

COMPUTERS AND INTELLIGENCE

Another area in which tremendous advances were made as a result of the war was that of computers. World War I was perhaps the first war in which a large amount of information had to be moved as quickly as possible, and for this, a good communication system was needed. And of course, the need became even greater in World War II. Not only was there a need for communication about the movement and direction that various troops, squadrons, and so on should take, but it was also important to keep this information from the enemy. This meant that it had to be enciphered, which soon set off a race between code breakers and code makers. Codes became more and more complicated, and soon they could only be deciphered by machines, namely computers. Work on computers had begun before the war, much of it in Germany. The German engineer Konrad Zuse had built a simple computer that he called the Z1 in 1936. He continued to work on it during the war, improving it significantly. A similar device, eventually called Mark I was being built in the United States.
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The war, and particularly a need for decoding enemy ciphers, soon created a demand for larger and faster computers. The Germans had begun using a coding machine called Enigma. Enigma allowed an operator to type a message then scramble it using notched wheels or rotors, each of which contained the letters of the alphabet. There were twenty-six electrical contacts on each side of the wheels corresponding to the letters of the alphabet. When a message was typed in, it was sent to the second wheel via electrical contacts, but contact was made at a different position on the second wheel, so a given letter, such as C, would be given a different designation, such as Z. Contact was then passed from this wheel to a third wheel, and again contact was made at a different position. In the earliest models, three wheels were used, but more wheels were added, making it even more complicated. With such a setup, it was almost impossible for someone to decode its messages. Furthermore, the codes could be changed each time the machine was used. Decoding was simple for the receiver, however; he merely had to set his machine up in the same way as the sender's machine.

Polish intelligence was the first to break the code; with the help of a German spy and using some complicated mathematics they managed to break the code in 1932, and they continued to decode German messages up to 1939. With the outbreak of the war, however, the Germans increased their security by making the system ten times more complicated. It was now beyond the Poles, so they handed everything they knew over to the British code breakers. The British code-breaking unit, codenamed Ultra, was set up at Bletchley Park in Sussex.

The British began working on the code, but they made little progress
until Alan Turing joined the group. In addition to mathematics, he had studied cryptology at Princeton, where he had obtained his doctorate, so he was well-equipped to tackle the enigma code. He soon built a machine he called the bombe, which cracked the code. The bombe searched for possible “correct” settings of the Enigma that had sent the message. Billions of possible settings had to be searched, but his machine was fast (for this time), and it would eventually narrow in on the correct setting. But there was a problem: Turing and company were allowed to build only a few bombes, and large numbers were needed to decipher all the incoming German messages. Turing and his coworker Gordon Welchman were frustrated and didn't know what to do. Finally, against all rules, they wrote directly to Winston Churchill. Churchill replied immediately, giving priority to their request. Over the next few years over two hundred bombes went into operation.
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