Or, more specifically, the caterpillar tractor invented in 1904 by Benjamin Holt. Since the 1880s, Holt’s company, based in Stockton, California, had manufactured massive, steam-powered grain harvesters. To allow the heavy machines to traverse the steep, muddy inclines of fertile river deltas, Holt instructed his mechanics to replace the drive wheels with “track shoes” made from wooden planks.
Later, Holt sought to sell his invention to government agencies in the United States and Europe as a reliable means for transporting artillery and supplies to the front lines during wartime.
One person who saw the tractor in action was a friend of Col. E. D. Swinton of the Engineering Corps of the British Army. He wrote a letter to Swinton in July 1914 describing “a Yankee machine” that “climbs like hell.” Less than a year later, Swinton drafted specifications for a tank—with a rhomboid shape and caterpillar treads—designed to cross wide trenches. It later became known as “Big Willie.” The tanks made their combat debut during the Battle of the Somme on September 15, 1916.
As historian Reynold Wik has noted, “the first military tanks had no American parts, neither motors, tracks, nor armament. However. . . the technological innovation which occurred in Stockton in November 1904 had proved that heavy machines could be moved over difficult terrain with the use of track-type treads.”
Camera: Aerial photographic reconnaissance came of age in World War I, thanks to higher-flying planes and better cameras. Initially, planes were deployed to help target artillery fire more accurately. Later, they were used to produce detailed maps of enemy trenches and defenses, assess damage after attacks and even scout “rear echelon” activities to glean insights into enemy battle plans. Baron Manfred von Richthofen—“the Red Baron”—said that one photoreconnaissance plane was often more valuable than an entire fighter squadron.
The opposing armies took measures to thwart photographic reconnaissance. Potential ground targets were disguised with painted camouflage patterns. (The French, naturalment, enlisted the help of Cubist artists.)
Of course, the most effective countermeasure was to mount guns on planes and shoot down the observation aircraft. To provide protection, fighter planes escorted reconnaissance craft on their missions. The era of the “dogfight” began—and with it the transformation of the airplane into a weapon of warfare.
Chlorine: Historians generally agree that the first instance of modern chemical warfare occurred on April 22, 1915—when German soldiers opened 5,730 canisters of poisonous chlorine gas on the battlefield at Ypres, Belgium. British records indicate there were 7,000 casualties, 350 of which were lethal.
German chemist Fritz Haber recognized that the characteristics of chlorine—an inexpensive chemical used by the German dye industry—made it an ideal battlefield weapon. Chlorine would remain in its gaseous form even in winter temperatures well below zero degrees Fahrenheit and, because chlorine is 2.5 times heavier than air, it would sink into enemy trenches. When inhaled, chlorine attacks the lungs, causing them to fill with fluid so that the victim literally drowns.
In response, all sides sought even more lethal gases throughout the remainder of the conflict. Chlorine was an essential ingredient in manufacturing some of those gases—including the nearly odorless phosgene, which was responsible for an estimated 80 percent of all gas-related deaths in World War I.