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.1
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.2
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.3
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.4
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.5
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.6
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.
A new and significantly better system was developed and put into operation in January 1941. It was called the ground-controlled intercept (GCI) system. In this system the antenna was rotated, allowing for a two-dimensional representation of the airspace around the operator. Incoming aircraft appeared as bright dots on a screen, similar to what we see today. The indicators, which were called plane positive indicators (PPI), were a significant improvement over those used in CH. The position and altitude of a plane could now be determined quickly.
Then, in 1939, Edward Bowen and his team developed a small radar system that could be used in airplanes and submarines. It was called the Air Interception (AI) system. It was quickly placed in many of the British aircraft and submarines, and it gave an even better fix on incoming German planes. The Germans tried to avoid it by flying only at night and in poor weather. This had no effect on the radar system, although the British pilots sent out to attack them had more trouble locating them.
In early 1940, however, the cavity magnetron was invented by John Randall and Henry Boot, and it revolutionized radar. It had been known for years that if short-wavelength radiation could be used in radar systems, it would significantly improve the images. But as they decreased the wavelength, the power of the system decreased. This changed with the introduction of the magnetron. With it, “centimeter” radar was possible for the first time, and the power of the new units was much greater. There was still a problem, however; large numbers would be needed, and Britain was in no position to develop and produce them. As we saw earlier, this led to the Tizard Mission in September 1940, which resulted in the manufacture of a large number of magnetrons in the United States.7
High-quality radar units could now be mounted in airplanes, ships, and submarines, and they were extremely effective. With their high resolution they could detect objects as small as submarine periscopes. And this quickly blunted the effectiveness of the German U-boat program. Large numbers of U-boats were hunted down and sunk, until finally the Germans withdrew their fleet.
Further advances in radar continued throughout the rest of the war. In 1938 the coastal defense (CD) system was developed. It was not an airborne radar unit, so it could be made much more powerful.
Several defenses against radar were developed during the war, and they were used by both sides. Radar “jammers” were developed that transmitted radio signals of the same frequency as the radar. The jammers were used to saturate the receiver with strong signals so that it couldn't detect properly. “Chaff” was also used. It was a cloud of lightweight strips of metal of a specific size that potential radar targets could deploy to interfere with the incoming signal. The radio receiver would only see a huge cloud when it was used.
But luckily for the British, the Germans didn't take radar very seriously, and they never put a large effort into developing it or protecting against it.
THE BATTLE OF BRITAIN
Soon after France surrendered, Germany turned its attention to England, and what took place over the next couple of months was one of the most famous battles of World War II. And it was totally an air battle. Hitler knew that for total control over Europe he would eventually have to attack England. In particular, he would have to land large numbers of troops on British shores. But while they were landing they would be under constant attack from Britain's powerful navy and also from its air force. He knew that the losses would be staggering and that he had to disable the RAF (Royal Air Force) and the navy before beginning his Operation Sea lion, which was his code name for the land invasion of Britain.8
Hermann Göring, the commander-in-chief of the Luftwaffe, assured Hitler that his airplanes could defeat the RAF in the south of England within four days and destroy the rest of the RAF within four weeks. Hitler was therefore overcome with confidence, and he scheduled Operation Sea lion for September 15. And there was no doubt that Germany had an overwhelming superiority in numbers: over 4,000 aircraft compared to Britain's 1,660. Included in this number for the Germans were 1,400 bombers, 800 fighter planes, 300 dive bombers, and 240 twin-engine fighter bombers. The RAF had mostly Spitfires and Hurricane fighters.
The battle began on July 10, 1940, with the Luftwaffe bombing coastal shipping centers and ship convoys. But by the end of July, British fighters had shot down 268 German planes and had lost only 150. As a result, the Luftwaffe switched to attacking airfields, operation rooms, and radar stations. They hoped, in particular, to disable the British radar system. The Stuka had been used extensively in the German blitzkrieg attacks, and it had been particularly effective when used over Poland, France, and Belgium, where there was little defense against it. But it had never encountered a fighter like the Spitfire, which had a top speed of 350 miles per hour compared with the Stuka's top speed of approximately 200 miles per hour. Furthermore, the Stuka was much less maneuverable, and its ability to dive was not an advantage in an air war. By the middle of August, nearly all the German Stukas had been destroyed by Spitfires and Hurricanes. Göring quickly pulled the few remaining ones out of the war.9
Britain's big advantage (aside from radar): the Spitfire. It was faster and more maneuverable than most German planes.
Germany may have had an advantage in numbers, but Britain had several important advantages. German fighters barely had enough fuel to get to England and back; they were used to protect the bombers, but they had to return soon after the bombers were over England, and this left the bombers vulnerable to attack. As a result, large numbers were shot down. Furthermore, German fighters frequently ran out of ammunition over England and had to head for home quickly. British planes could easily land and quickly reload their guns. And of course the biggest advantage the British had was their radar detection system. The RAF therefore knew at all times where the German bombers and fighters were, but the Luftwaffe pilots could only guess where the British were.
After August 23 the Luftwaffe stopped attacking seaports and radar sites and switched to night raids on cities—London, in particular. But the Germans continued losing planes at a rate of almost two to one: 1,000 German planes to 550 of the RAF's planes. And on September 15 the Luftwaffe lost sixty planes to the RAF's twenty-eight in a single day. Two days later Hitler postponed the invasion of Britain indefinitely. But the indiscriminate bombing of the larger cities continued. In the end, both sides had taken heavy losses, but the German losses were much greater. And finally, about the middle of October, the raids ceased except for an occasional bombing. The Battle of Britain was over and the British had won. But the war was far from over.
AMERICAN ENTRY INTO THE WAR
The United States entered World War II following the Japanese bombing of Pearl Harbor, but even before 1939 most Americans realized they would eventually be involved in the war in Europe. The trigger, however, came on December 7, 1941. Over a period of four hours six Japanese aircraft carriers sent waves of torpedo planes, fighters, and dive bombers over Pearl Harbor. Given the simmering political tensions between the United States and Japan, there was some expectation among American military leaders that the Japanese might attack. Nevertheless, the US forces were caught completely off guard. As a result, the Japanese planes were able to destroy or severely damage eight battleships, ten smaller warships, and two hundred thirty aircraft, while killing 2,400 US personnel.10
The following day the United States declared war on Japan, and since Hitler and Mussolini had just signed a pact with Japan, Germany and Italy declared war on the United States. Although Japan didn't follow up its attack on Pearl Harbor, it did attack the US air base near Manila in the Philippines, and the Japanese army invaded and trapped large numbers of Americans and Filipino forces in nearby Bataan, leading to the infamous Bataan Death March, during which thousands of Americans and Filipinos died. General Douglas MacArthur escaped to Australia and vowed to return. The Japanese continued their invasion, seizing the Dutch East Indies, and then the islands of Tulagi, Guadalcanal, and the Solomon Islands. They seem almost unstoppable.
What was left of the United States Navy first met the Japanese in the Coral Sea near the Solomon Islands. During two days of combat the Japanese lost a small carrier, a destroyer, and several smaller ships, but the United States lost a carrier and a destroyer, so the battle has generally been considered a draw. But in the process the Americans stopped the invasion of an island that would have allowed the Japanese to strike Australia. It was also an important battle in that the Americans learned a lot about Japanese tactics, and this would help them later in the war.
One of the major naval battles of the war came in June 1942. The Japanese admiral Yamamoto was planning a large offensive near Midway Island. He hoped to trap and destroy most of the American fleet in a quick and decisive battle, but American intelligence, which had managed to decode Japanese messages, knew what he was planning. This allowed American admiral Chester W. Nimitz to set up a web of decoy tactics and plan an ambush. And when the battle ended, the Japanese had lost four carriers and all the airplanes that had attacked Pearl Harbor, along with a large number of Japanese pilots. In turn, the Americans had lost only one carrier. This was a major defeat for the Japanese, and a turning point in the war in the Pacific. The American navy now had clear-cut superiority over Japan's navy.
The battle of Leyte Gulf in the Philippines, which came in October 1944, was one of the largest naval battles in history. It was also a decisive victory for the US Navy, which sank most of the remaining Japanese fleet. What remained of the Japanese navy finally retreated back to Japan.
Over the previous few years Japan had occupied a large number of islands in the South Pacific, and American forces began a strategy known as island hopping, in which they targeted islands that could support airstrips that would allow them to get closer and closer to Japan itself. At the same time they applied their air power to cut off all supplies to Japanese troops on the various islands. The Japanese, however, had dug in, and many of them were in bunkers and caves. Furthermore, American marines soon found that most Japanese preferred to fight to the death rather than be captured. So the fighting was difficult.
Hand-fought battles at Guadalcanal, Tulagi, the Marshall Islands, Iwo Jima, and Okinawa followed. In most cases the Japanese fought until the last man was killed. Furthermore, Japanese pilots were now flying kamikaze missions in which they would commit suicide by flying their planes into American ships. In this way they managed to sink thirty-eight ships and damage many others.
Because of this, the American high command decided that an invasion of mainland Japan would lead to the loss of too many American lives, with the Japanese refusing to the end to give up. President Truman therefore ordered the dropping of atomic bombs on Hiroshima and Nagasaki in August 1945, and within a short time the Japanese surrendered. We will discuss this in more detail in the next chapter.
Turning now to the war in Europe, the first American operation was in November 1942, when American and British troops landed in North Africa. They stopped the German advance on Tunisia, and by May 1943 they had defeated the Germans, capturing over 275,000 men in the process. Along with the British, they then turned to what they believed to be the weakest link of the German and Italian defense, namely Sicily. In July 1943, a large amphibious invasion was unleashed, and in a little over a month Sicily was under Allied control. The Allies then turned their attention to the Italian mainland. American troops landed in Italy in September, and Italian troops surrendered almost immediately, but a large number of German troops were now in Italy, and they continued to fight through the winter. But in June 1944, Rome fell, and soon the Allies had occupied most of Italy.
Meanwhile, in England the largest amphibious attack in history was being planned. The operation, which began on June 6, 1944, consisted of 4,600 ships and over a million troops. Under the command of General Dwight D. Eisenhower, the Allies crossed the English Channel in an effort to establish a beachhead in Nazi-occupied France. The Germans had been expecting an invasion, but they didn't know where the Allied forces would land. For two months preceding the invasion British-based aircraft had bombed airfields, bridges, and rail lines throughout France. And on the night before the landing, paratroopers were dropped inland as naval guns powdered installations along the shorelines. The various landings were given code names; the British and Canadians landed at Gold, Juno, and Sword Beaches, while the Americans landed at Utah and Omaha Beaches. The Canadian and British landings went relatively smoothly, meeting little opposition, but the Americans were met by heavy German gunfire that inflicted many casualties. Within five Days, however, sixteen Allied divisions were in Normandy, and the drive to liberate Europe was under way. By August 25 Paris was captured, as the Allies continued their push toward Berlin.
In the east, the Soviets, who had beaten back a German invasion, were also pushing toward Berlin. Although it was now almost certain that Germany would soon be defeated, the Germans didn't give up easily, and in December 1944 they launched a massive counterattack in the Ardennes Forest that caught the Allies off guard. This engagement became known as the Battle of the Bulge because of the large bulge it created in the Allied lines. By late January, however, with large numbers of Allied reinforcements rushing to the front, the German offensive was stopped. And in March, Allies crossed the Rhine River and began a final push toward Berlin. The remaining German forces were now being squeezed from the east and the west. On May 2, 1945, the Germans surrendered.
ADVANCES IN AVIATION
Let's go back now and look at some of the important advances that were made during the war, many of which depended on physics. Major advances in aircraft design occurred, with the most important being the building of the first jet plane. Aside from the first jet plane, however, there were significant advances in traditional aircraft. Let's begin by looking at some of the major planes that were used in the war, and there capabilities. The British Spitfire was, without a doubt, one of the best. It was used very successfully against the Luftwaffe in the Battle of Britain. It had a maximum speed of approximately 350 miles per hour, and it performed well in climbs; furthermore, it was relatively easy to fly. The British Hurricane was also an excellent plane, and it was also used extensively in the Battle of Britain.11
The German Messerschmitt 109 was the only German plane comparable to the Spitfire. It had a maximum speed slightly less than that of the Spitfire, and it was less maneuverable, but it was faster in a dive.
The Japanese Mitsubishi Zero was the primary Japanese naval plane. It was used in the attack on Pearl Harbor and throughout the Pacific war. In the early years no American plane was a match for it. By late in the war, however, it was no match for most American planes.
The P-51 Mustang was one of the best American planes. It had a top speed of 370 miles per hour and was a favorite among American pilots. Many considered it the best fighter plane of the war. Its speed, maneuverability, and range made it an excellent aircraft. Another of the American planes was the Lockheed P-38 Lightning. It is said to have shot down more Japanese planes than any other American fighter during the war. It had a top speed of 414 miles per hour. Another excellent American plane was the F4U Corsair, which was used by US naval and marine pilots. It was the first plane to finally give Americans superiority over the Japanese zero, as it was much faster and had a better roll rate. Its maximum speed was 435 miles per hour.
The fastest and most interesting plane of the war, however, was the Messerschmitt Me 262, which was the world's first jet plane. It had a maximum speed of about 530 miles per hour, which was 93 miles per hour faster than the swiftest Allied fighters. Fortunately for the Allies, it came into the war relatively late, and only a few were built, so it had little impact. Nevertheless, German pilots of the Messerschmitt Me 262 shot down approximately 540 Allied planes, and they were so fast that they were difficult targets. They were so fast, in fact, that German pilots had to learn new tactics when using them in combat. Allied pilots soon found that the best way to deal with them was to attack them on the ground or during takeoff or landing. Airfields in Germany that were identified as jet bases were therefore heavily bombed. The Me 262 did have a number of drawbacks, however; it used twice as much fuel as a conventional aircraft, and near the end of the war, Germany was running short on fuel. Furthermore, there were engine reliability problems.
The jet engine was invented by two different inventors at about the same time: Hans von Ohain and Frank Whittle. Frank whittle was the first to patent a turbojet engine; in fact, his patent came in 1930, six years before Ohain's. But neither man knew anything about the other's work. But it was Ohain who was first to build a workable jet plane.
Whittle was a pilot and an English aviation engineer who joined the RAF in 1928. At the age of twenty-two he came up with the idea of using a jet turbine to power an aircraft, and he began construction of a jet engine in 1935. It was tested in 1937, and an airplane using his engine first flew in 1941.
Like Whittle, Ohain was only twenty-two when he conceived the idea of a jet-propelled aircraft. His design was similar to Whittle's, but it differed in the internal arrangement of the parts. An airplane using his design for an engine was first flown in 1939. So both Germany and England actually had jet engines before the beginning of the war. But only Germany used the technology for a new type of fighter before the end of the war.
Details of a jet engine.
Jet engines operate as a result of Newton's third law, which states that for every action there is an equal and opposite reaction. The opposite reaction is what gives the thrust that pushes the jet plane forward. The easiest way to visualize this is to blow up a rubber balloon and let it go. You see immediately that it flies off in an array of flips and loops as the air forces its way out of the balloon. In short, as the air pushes its way out, it forces the deflating balloon in the opposite direction. This is basically what happens in a jet engine.
Several different kinds of jet engines now exist, but we'll restrict our discussion to the turbojet. At the front of the turbojet is an inlet that allows air to enter. Once inside, the air is compressed by blades that squeeze it into a much smaller volume. From here it is forced into what is called the combustion chamber. With the increase in pressure, the temperature of the gas goes up until it reaches over a thousand degrees Fahrenheit. Fuel is then sprayed into the air, and the mixture is ignited. This causes it to heat even more dramatically, and it leaves the combustion chamber, or combustor, with a temperature of about three thousand degrees Fahrenheit. The resulting heated gas exerts a large force in all directions, but it exits only at the rear of the engine, and this gives the plane a tremendous forward thrust. As the gas leaves the engine it passes through a series of blades that constitute the turbine, which rotates the turbine shaft. The turbine shaft, in turn, rotates a compressor that brings in a new supply of air. Thrust can be increased with the use of what is called an afterburner, where extra fuel is sprayed into the exiting gases, which burn to provide additional thrust.
THE FIRST ROCKETS IN WAR
Not only was the first jet introduced in World War II, but so was the first large ballistic rocket. Much of the technology, however, had already been developed by the physicist Robert Goddard. Goddard is now often referred to as the father of modern rocket propulsion, and the NASA Goddard space Center in Maryland is named after him. Most of his work took place at Clark University at Worcester, Massachusetts, where he was head of the physics department. In 1926 he constructed and launched the first rocket using liquid fuel. Earlier, in 1914, he had patented both liquid rocket fuel and solid rocket fuel. He made many contributions to rocketry, including a gyroscope control, power-driven fuel pumps, and vanes on the exterior of the rocket to help in its guidance. And he was the first to show that a rocket would work in vacuum and that it didn't need air to push against.
Early in World War II the Germans became interested in the possibility of using rockets as weapons. Artillery Captain Walter Dornberger was assigned the job of determining how effective they would be. While looking into the problem, a young engineer by the name of Wernher von Braun came to his attention, and he hired him as head of his rocket artillery unit. By 1934 von Braun had a team of eighty engineers working for him, and operations were moved to Peenemünde, on the Baltic coast. Hitler now began taking an interest in the project.
Wernher von Braun.
Von Braun and his team had many problems to overcome. Rockets look rather simple, but a lot of science, particularly physics, is needed to make them work properly. The V-2 that von Braun was building could reach an altitude of almost seventy miles, and at this altitude there is almost no air. And the rocket fuel needed an ample supply of oxygen for it to burn. This meant that oxygen had to be added to the propellant. The V-2 used a 75 percent ethanol-water mixture for fuel and liquid oxygen as an oxidizer.12
Rockets are propelled in the same way jets are propelled. They also work because of Newton's third law, and again it's the reactive force that produces the thrust. It's also important to note that the rocket flight consists of several phases: launch, thrust, cruise, and crash. Actually, the first phase (launch) is when the rocket is sitting on the launch pad, so it's not moving. At this point there are two forces acting on it: the weight of the rocket downward, and its reaction force acting back from the pad. These two forces are equal and opposite.
The thrust phase begins when the rocket engine begins firing. At this time there will be three forces acting on the rocket: the weight of the rocket, the thrust provided by the engine, and a drag force that is a result of air resistance. If we now apply Newton's second law, which states that force equals mass times acceleration, we get Fthrust − Fdrag − wt. = ma, where m is mass, a is acceleration, and wt. is the rocket's weight. There is a small problem here, however: the mass of the rocket changes as a rocket moves upward because fuel is being burned. But this was easily overcome by early engineers.
Rocket, showing thrust, drag, and weight.
The blast from the engine will eventually stop at some point, and the rocket will enter the cruise phase. During this time there is no longer an upward thrust on the rocket, and it is on its own. It will continue gaining altitude for some time after its engines are shut down because of its velocity, but eventually it will reach its maximum altitude and begin falling back to earth, and because of gravity it will accelerate according to the formula a = (wt. − Fdrag) / m. Thus, except for drag, it will drop like a falling stone. In reality, of course, the rocket is not going straight up and down, it is also moving horizontally, so its path will generally be similar to that of an artillery shell.
In a liquid-fueled rocket, the propellant and oxidizer have to be kept in separate tanks before the combustion. Oxygen is then combined with the fuel, with mixing taking place when the oxygen and fuel are sprayed into the combustion chamber. The ignition gases exit through a nozzle at the lower end, producing the thrust. These gases are at a very high temperature, so the nozzle has to be cooled. In early rockets the exhaust was cooled using alcohol and water.
The rocket also had to be stabilized once it was in flight, otherwise it would tumble uncontrollably. Two types of systems have been used for this: active and passive. Active elements are movable and passive are fixed. Of critical importance is the center of gravity of the rocket. It is important because all objects, including rockets, move around their center of gravity when they tumble. The center of gravity is the same as a center of mass, namely the point where all the mass can be considered to be concentrated.
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.13 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.14 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.15
Alan Turing.
Enigma was used by the German navy, army, and air force, but the German high command used another, even more complicated encoder called Lorentz. It was introduced in 1941, and it used twelve wheels. The only way to break its code was with the use of a very large computer, much larger than anything that had ever been built. It would be a huge undertaking, but the information it could supply would be of tremendous value. The design engineer was Tommy Flowers, and the prototype, called Colossus Mark I, was produced in December 1943. It was in operation by February 1944.
With the Colossus, the messages sent by the Lorentz machine could be decoded, and over the next few months a large amount of German intelligence was intercepted and decoded. The Colossus, along with Turing's bombe, no doubt helped to shorten the war.