The Physics of War (28 page)

The British were therefore ready when Germany resumed submarine warfare in January 1917. Less than three months later the United States entered the war, and by then another technique had also been developed to protect ships from submarines: the use of convoys with destroyer escorts. A submarine was lucky if it could sink a single ship of the convoy, and when it tried, it was in constant danger from depth charges. In addition, large numbers of mines were laid at depths up to six hundred feet in the North Sea and in the region between Scotland and Norway. U-boats soon became completely ineffective.

THE FINAL HORROR—POISONOUS GAS

The stalemate was a serious problem for both sides; each wanted to attack but knew that it would be suicide unless some sort of new weapon was developed. In their frustration the German high command turned to the physical chemist Fritz Haber. He had helped them earlier with a problem related to their ammunition, and German leaders hoped he could help again. Was there something that could be fired into the Allied trenches that would force the troops in them to flee? Haber immediately thought of poisonous gas. Several German generals
had reservations, saying that the Allies would no doubt retaliate the same way, but Haber assured them that their chemical industry would have a hard time producing a similar gas. Despite these reservations, Haber was told to produce the gas. Haber decided on chlorine, and the Germans introduced it in April 1915, near Ypres. This region of the line was held by a combination of British, Canadian, French, and Algerian troops. Thousands of tanks containing chlorine were transported to the German lines. Fans were then used to blow the poisonous gas toward the enemy.
¹⁰

On the evening of April 22, 1915, French and Algerian troops noticed a large yellow-green cloud drifting slowly toward them. Puzzled, they became suspicious that it was being used to conceal offensive troop movements, and they stood their ground waiting for an attack. Within minutes the cloud was all around them, and they were choking and gasping for breath. The inhaled gas was destroying their respiratory organs. When they realized what was happening they began to panic, and many of them fled in disorder. Within a short time a four-mile gap was opened along the line. Strangely, though, the Germans were as surprised by the effectiveness of the gas as the French were. And although German troops did advance, they did so nervously and hesitatingly. They managed to seize some land, but the British and Canadians on the right fought valiantly, and in the end little was gained. But a new phase in the war had begun.
¹¹

The British press immediately condemned the attack and played up the incident, and other countries, including the United States, soon joined in. Despite the condemnation, though, the British immediately went to work on research into poison gases that they could use to retaliate. There was, however, a problem with the delivery of the gas. If the wind changed direction while it was being delivered, it could blow back upon the troops delivering it. And indeed this happened to both the British and German troops. A better delivery system was needed. Again, the German high command went back to Haber. Was there a poisonous gas that could be easily packed into artillery shells and exploded in the trenches? Haber and his team went to work immediately and soon came up with phosgene. It was similar to chlorine gas, but unlike chlorine it caused no coughing or choking while it destroyed the lungs. As a result, soldiers usually inhaled much more of it before they realized what was happening. As a weapon it was therefore much more potent.

Then Haber came up with the most dreaded gas of the war—mustard gas. The Germans used it for the first time against the Russians in September 1917. Mustard gas was almost odorless, and it caused serious blisters both internally and externally.

Each time the Germans developed a new poisonous gas, however, the Allies soon developed the same gas and used it on the Germans, so in the end it was of little advantage to either side. The Germans inflicted several hundred thousand casualties, but they suffered around two hundred thousand themselves, with about nine thousand deaths.
¹²
Toward the end of the war, however, there were few casualties, as gas masks had been developed.

Although Haber apparently never felt any guilt for his role in developing poisonous gas, his wife was so appalled at what he had done that she committed suicide. His close friend Albert Einstein also severely reprimanded him for his role in slaughtering so many fellow human beings. But in the end it backfired for him. He was of Jewish descent, and in 1933 he had to flee Germany as the Nazi's began rounding up Jews.

THE FIRST TANKS

Another attempt at breaking the stalemate came with the introduction of the first tanks to the battlefield in late 1916. The idea that an armored, bulletproof vehicle could be helpful in battle had been around for many years. Even Leonardo da Vinci designed one. But it was not until after World War I had started that the idea began to be taken seriously. The impetus came from a British officer, Colonel Ernest Swinton. While driving through northern France in October 1914, having seen the large number of casualties inflicted by modern weaponry, he began to think about how troops could be better protected. A friend had mentioned a vehicle he had seen with large caterpillar tracks, and he suddenly realized that it would be extremely helpful to build a bulletproof military vehicle with caterpillar tracks.
¹³

In November he talked to Lieutenant Colonel Maurice Hanley about the idea; Hanley, in turn, sent a memo to the Committee of Imperial Defense. The army, however, had little interest in the new device. Swinton therefore organized a demonstration of a caterpillar-track device for several high-ranking dignitaries in June 1915. In attendance were Lloyd George (minister of munitions, who would eventually become prime minister) and Winston Churchill, the first lord of the admiralty. Both were impressed, and Churchill immediately established what he called the Landships committee to look into the building of such a device. It didn't take long for the committee to decide the new device could be helpful in the war effort, and they agreed to go ahead with the design and building of a prototype model. It was important to keep it secret, so they codenamed it “tank,” so the Germans would not know what it was. And of course, the name stuck.
¹⁴

Swinton was hired as an advisor, and he suggested several criteria for the new vehicle. It had to have a minimum speed of four miles per hour; it had to be able to cross a four-foot trench and pass easily through barbed wire; and it had to be capable of climbing over objects five feet high. In addition, it had to be bulletproof, and it had to have two machine guns. When it was finally built it was nicknamed “Little Willy.” It didn't quite live up to Swinton's criteria, but it was close. It could move at a rate of about three miles per hour on level ground; it weighed fourteen tons and had a twelve-foot-long track frame; and it was rhomboid shaped and could carry three people. In early tests, however, it had problems crossing trenches, but this was soon corrected in a slightly larger model called “Big Willie.” Of particular interest was that these tanks were produced by the navy rather than by the army.

Everything was now ready for the production of combat models, and the first combat model, called the Mark I, was demonstrated in June 1916. Lloyd George was impressed enough to order the immediate production of full-size tanks. In the meantime, the French had heard of the English plans and had begun work on their own tank.

The Mark I was ready for battle in September 1916, with thirty-six having been completed. Several military leaders, including Churchill, urged complete and thorough testing before it was used, but others wanted to use it as soon as possible. At the time the battle of Somme was in progress in France, and it hadn't gone as well as the British had hoped. As a result there was pressure to begin deploying the tanks. Thirty-six tanks therefore lined up on the front lines at Flers in France in September, and their appearance no doubt stunned the Germans. But Churchill was right: they were not ready. Many of them broke down in the initial attack, and some of them got stuck in the mud, so aside from the shock value, they were not very effective.

Meanwhile the French, having produced 128 tanks by April 1917, took them into battle, but as in the case of the English tanks, they were also not ready, and several problems developed. The first really successful use of tanks came on November 20, 1917, at the Battle of Cambria. With a force of 474 tanks the British attacked the German lines and breached a twelve-mile stretch. In the process they captured ten thousand German soldiers and a large number of machine guns. Surprisingly, though, the Germans did not try to emulate their attackers; they were slow in coming up with their own plans for a tank. One of the reasons, no doubt, was a lack of resources at this stage of the war.

The British and French, on the other hand, poured all their resources into the production of tanks. By the end of the war, the British had built 2,636 and the French had built 3,870. In addition, the United States built eighty-four tanks.
The Germans, on the other hand, only produced twenty, but they did develop weapons that were fairly effective against it.

All in all, the British Mark I performed fairly well considering the conditions. Most battlefields were littered with huge craters and strewn with barbed wire. The Mark I was able to move quite effectively over the very rough terrain, and it could easily cross trenches and craters of up to nine feet, and it had no problems with barbed wire. Indeed, it could even knock down small trees.

AMERICA ENTERS THE WAR

The beginning of the end began at the Eastern front, where the Russians had been fighting the Germans for two and a half years. They had suffered several defeats and morale was at an all-time low. The Russian army was in shambles, and the government back home was falling apart. As a result, in March 1917, Czar Nicholas was removed from power and a provisional government was set up. Surprisingly, though, despite the problems and setbacks the war had created, the new government vowed to fight on. But by now the Russian army was starting to fall apart; desertions were becoming more and more common, until finally the generals decided that they had had enough. Seeking peace, the Russians signed the Treaty of Brest-Litovsk.
¹⁵

Germany was now able to send large numbers of troops to the Western front. They began arriving at the rate of ten divisions a month, and with the new build up, German high officials decided it was time to hit the Allies with a decisive blow so overwhelming that they would quickly agree to end the war. And on March 21, 1918, they struck. Within days a huge gap was opened up between the British and French lines. The Germans pushed forward, trying to take advantage of it, but they were surprised by the resolve and stubbornness of the British troops. They held their line. Meanwhile, the United States had declared war on Germany, and American troops were now coming across the Atlantic in large numbers.

For years President Woodrow Wilson had argued that the United States should stay out of the war, and most Americans agreed with him. But after the sinking of the
Lusitania
(with 128 Americans aboard), many Americans were angered, but Germany quickly stopped U-boat attacks, causing the anger to subside. On January 31, 1917, however, Germany decided to restart their unrestricted war on all shipping vessels in the war zone, neutral or not. President Wilson was stunned by the news, but the United States refrained from declaring war. But in February and March German submarines sank several American
ships. In addition, British intelligence had intercepted and decrypted a message from Germany to the Mexican government. The Germans were promising Mexico that in return for its support all territories it had lost to annexation by the United States would be returned. These territories included Texas, New Mexico, and Arizona.

On April 2, 1917, Wilson asked Congress for a declaration of war, and it was quickly granted. The first American troops began crossing the Atlantic a few months later. A contingent, commanded by General Pershing, landed in France in June. The Germans were still attacking the Allied line, but now with considerably less success. And soon they were facing the first American troops.

A uniform Western command was formed in April 1918 that included British, US, and Belgian troops under General Foch. In the meantime the number of Americans in France doubled in March, and then it doubled again in May and August. The Germans attacked again in July but were quickly pushed back by a counteroffensive. The British then advanced in the north, and the Americans went on the offensive throughout the Argonne region of France. On July 18 Foch's forces along with the French went on the offensive along with nine double-strength American divisions. The Germans began to weaken, and then on August 8, over four hundred British tanks faced them. Soon they were surrendering by the thousands. And Germany's allies began to surrender: first there was Belgium in September, then Turkey on October 30, and finally Austria-Hungry on November 4. German morale plummeted as its resources also began to collapse, and finally, on November 11, 1918, the Treaty of Versailles was signed, ending the war.

Electromagnetic radiation has played a large role in warfare since World War I, especially as used in radar, radio, and lasers. To understand these technologies, however, we have to go back several years before the beginning of World War I.

THE PRODUCTION AND DETECTION OF ELECTROMAGNETIC WAVES

James Clerk Maxwell is regarded by many as one of the most important physicists ever born. His prediction of the existence of electromagnetic waves led to major advances in science and also to important changes in everyday life.
¹

In the mid-1800s, four basic things were known about electricity and magnetism:

• All electric charges are surrounded by an electric field. The direction of the field is such that like charges repel and unlike charges attract.
  
• Magnetic poles of two types exist, referred to as north and south, and they always exist together.
  
• A changing electric field (or a charge) generates a magnetic field.
  
• A changing magnetic field generates an electric field.
  

These facts were known before Maxwell's time. His contribution was to put them in mathematical form and show that electricity and magnetism are intimately related, together forming what we call an electromagnetic field. In particular, oscillating electric charges produce an electromagnetic field that moves out from the charges, and the waves produced have both an electric and a magnetic field associated with them. Of particular importance, Maxwell
found that electromagnetic waves traveled at the speed of light, and he proposed that light itself was an electromagnetic wave. Furthermore, he pointed out that electromagnetic waves of higher and lower frequencies (frequency at which the charge was oscillating) would likely lie beyond the frequency of light. In other words, there should be an array of electromagnetic waves of all different frequencies. And indeed, we now know that this is the case.

His prediction was made in the 1860s, and it wasn't long before electromagnetic waves were detected directly. In August 1879 the German physicist Heinrich Hertz built a simple device in his lab that he believed could be used to detect Maxwell's waves. It consisted of a loop of wire with a gap to which small brass knobs had been attached. The loop was connected to an induction coil so that a spark could be generated across a gap. He then built a second loop with an induction coil to act as a detector. When the first loop was connected to the induction coil, a spark jumped across the gap, sending out a “signal.” This signal was detected by the second loop (the receiver), which was nearby. Hertz was able to show that the signal exhibited a wave nature, and that it had a certain wavelength, or frequency, so it was obviously another electromagnetic wave. Furthermore, he was able to calculate its speed, showing that it was equal to the speed of light. He announced his discovery in 1887, claiming it was a verification of Maxwell's prediction.

Hertz's apparatus for detecting electromagnetic waves.

THE ELECTROMAGNETIC SPECTRUM

Maxwell was right: there was, indeed, a large spectrum of electromagnetic waves. We now know that they range from very short wavelength (high frequency) gamma rays down to very long wavelength (low frequency) radio waves. In between these two extremes are x-rays, ultraviolet (UV) light, visible light, infrared radiation and microwaves. Furthermore, all of these waves carry energy, or, more exactly, they are a form of energy, and the magnitude of their energy depends on their frequency (number of vibrations per second).
²

The electromagnetic spectrum.

Several of these types of radiation had already been detected. In 1800 the German-born astronomer William Herschel was studying the temperatures of different colors by moving a thermometer along the spectrum of colors created by a prism when he noticed that the highest temperature was actually beyond red, which was at the end of the spectrum. He concluded that sunlight contained a heat-type radiation that could not be seen. We now know that this is infrared radiation. You can easily detect it when you turn on the burner of an electric stove. You feel the heat long before the burner turns red.

The following year Johann Ritter was looking at the other end of the visible part of the spectrum when he detected invisible rays that were similar to violet rays, but beyond them in the spectrum. He called them “chemical rays,” but their name was later changed to ultraviolet rays.

Also, years earlier, in 1895, Wilhelm Röntgen of Germany had noticed a type of high-energy radiation that was created when an evacuated tube was subjected to high voltage. He called the waves x-rays. And Hertz, in some of his earlier experiments, had already discovered microwaves and radio waves. Finally, in 1910 the British physicist William Bragg showed that there were very energetic waves with energies even higher than those of x-rays. These are called gamma rays.

Let's go back now and look more carefully at how we identify each of
these types of radiation. As we just saw, they differ in their vibration rate, or frequency. And since frequency is related to wavelength (the distance between equal points along the wave), they also differ in wavelength. In addition, they differ in how energetic they are (we will talk more about this later). For the most part we will identify them by their frequency. The unit of measure for frequency is the Hertz (Hz), which is the number of vibrations per second. The range in frequency, however, is so large that we sometimes have to use units such as megahertz (MHz), which is one million Hertz. Infrared light, for example, has a frequency of up to approximately 100,000 MHz. Microwaves, which you are no doubt familiar with in relation to microwave ovens, have a range from 1,000 to 100,000 MHz. And radio waves go from 1,000 MHz down to 50 MHz. For radiation of even higher frequency we have to use gigahertz (GHz), which is 1 billion Hertz. Infrared radiation is in this range. And finally, beyond infrared, through visible and UV light, a unit called the Terahertz (THz), or 1 trillion Hertz, is used.

Diagram of a wave showing wavelength and amplitude.

Almost all of these types of radiation have important applications to war. Radio waves are used extensively for communication, and, as we will see, radar played a critical role in World War II, and it is still used extensively. We will also discuss lasers; most lasers use visible light, but other radiation frequencies are now used to produce other types of lasers, and lasers have played an important role in the military. Infrared radiation also has an important application to the military in relation to various devices that are used for night vision. And finally, x-rays are, of course, critical in the treatment of wounded soldiers.

RADIO WAVES

Radio waves are one form of electromagnetic radiation, and it wasn't long after Hertz's discovery that scientists began experimenting with them. One of
the first to do so was Guglielmo Marconi (1874–1937) of Italy. When Hertz died in 1894 there was a sudden renewed interest in his discoveries and many newspapers published articles on them. Hertz's work came to the attention of Marconi, who was only twenty years old at the time. He was sure the waves Hertz had discovered could be used to create a system of wireless telegraphy, in other words, a telegraphic system that could send messages without using wires. As a result, he set up a simple system to see if this was feasible. His system consisted of a simple oscillator (a spark-producing radio transmitter) and a “coherer” receiver, which was a modification of an earlier receiving device. He used a telegraphic key to operate the transmitter so that it would send a series of long and short pulses (dots and dashes); a telegraphic receiver was activated by the coherer.
³

By the summer of 1895 he was able to transmit and receive messages over a distance of a mile and a half. He decided at that point that he would need funding to improve the device. Finding little interest in Italy, he traveled with his mother to England, where he demonstrated his device to William Preece, the chief electrical engineer of the British General Post Office. A series of demonstrations to government officials followed, and with their support, in March 1897, Marconi was able to send a message over a distance of 3.7 miles.

Marconi and his experiments began to attract international attention. In 1899 he set up equipment on two sides of the English Channel and sent a message from France to England. Shortly thereafter he sailed to the United States at the invitation of the
New York Herald
. In the following year he began working on equipment to send a message across the Atlantic, and on December 12, 1901, he claimed that he had accomplished his goal. There was, however, some skepticism, so in February 1902, he set up a more advanced apparatus and proved the skeptics wrong. There was no doubt that he had accomplished his goal.

One of the early problems for long-distance radio transmission, or at least anticipated problems, was the curvature of the earth. Since radio waves travel in straight lines, it was expected that this curvature would cut off the signal. Marconi was pleased to find this didn't happen. The reason was that the radio waves were reflected, or bounced, back and forth due to the presence of electrically charged particles in the atmosphere.

Marconi continued to work on his device over the years, but he soon discovered he had competition. His messages used a series of dots and dashes (Morse code), but in the early 1900s, the first vacuum tube was invented, and as a result, wireless voice transmission became possible. This new development quickly overshadowed telegraphic transmission.

Of particular interest, however, was that war departments on both sides of
the Atlantic were soon interested in Marconi's device. The British War Office was one of Marconi's first customers, and soon after major German telegraphic firms began buying his products; he set up a company in Germany to start selling them around 1900.

Radio soon started to play an important role in war. Over the next few years transmitters and receivers were improved significantly and radio became the major communication media during war. It was starting to be used by both sides in World War I, and it was, of course, used extensively in World War II.