In the early weeks of World War I the firepower of machine guns and artillery made above-ground operations so costly that trench warfare soon developed. Many ideas were tried in an effort to break the resulting stalemate. Lieutenant Colonel Ernest D. Swinton of the British army watched a Caterpillar tractor travel through mud and broken ground behind the lines and saw it as the basis for an armored vehicle. He took his idea to the Committee of Imperial Defence, but only Winston Churchill, then first lord of the admiralty, saw its possibilities.

Churchill put a Royal Navy group to work developing a “landship. (Because of this naval origin tanks retain such nautical terms as hatch, ports, hull, deck, bow, and superstructure.) As experiments continued in secrecy, parts made in different factories were labeled as parts for “tanks—presumably water tanks to be used in Russia or Mesopotamia.

Tanks were used in combat for the first time during the Battle of the Somme, September 15, 1916, but the surprise effect was wasted by employing only 49 vehicles in scattered groups. At Cambrai, November 29, 1917, the British used 378 tanks backed by six infantry divisions and penetrated six miles (10 km) into the German defenses. The U.S. Tank Corps, using French tanks, was first in action at St. Mihiel, on September 12, 1918.

The first British tanks were 34 feet (10 m) long, each with a crew of 11 manning two 6-pounder guns (cannon) and five machine guns. Top speed was 6 mph (10 km/h). The French developed the Renault light tank with a crew of two. Tanks were used as moving forts to protect infantry following close behind.

After the war B. H. Liddell Hart and J. F. C. Fuller in Great Britain, Heinz Guderian in Germany, Charles de Gaulle in France, and Adna R. Chaffee in the United States advocated use of tanks in masses for shock effect and to avoid the costly stalemate of trench warfare by restoring mobility to land forces. Conservative military men were slow to accept this concept. They considered the tank an auxillary weapon to be used in support of infantry.

In Germany, however, the theories of Liddell Hart and the other early tank planners were put into practice under Adolf Hitler, and there was created a powerful armored force capable of decisive action.

By World War II, armies had developed three principal kinds of tanks—heavy (27 to 41 metric tons), medium (14 to 27 metric tons), and light (6 to 14 metric tons). Heavy and medium tanks were designed for battle, while light tanks were designed for reconnaissance as a mechanized equivalent of cavalry. The heavy tank was the most heavily armored and least vulnerable, but because of its slowness and lack of maneuverability, it had to be supported by lighter and faster medium tanks. In World War II, the bulk of the tank forces was composed of medium tanks.

The theories of the tank strategists proved their worth in 1939 when Germany defeated Poland in.36 days using panzer (armored) divisions as spearheads to exploit every breakthrough. This use of armor, combined with air power and rapidly moving infantry, was called blitzkrieg (lightning war).

In the same manner Germany defeated France in a matter of weeks in 1940. A rapid thrust across France by German panzer forces, spearheaded by a tank corps led by General Guderian, was the decisive factor.

The first great battles in which both sides used tanks as their primary weapons took place in the deserts of North Africa. The German commander in North Africa, General Erwin Rommel, proved to be World War II's greatest tactician in armored warfare as he repeatedly defeated far larger and stronger forces sent against him.

The largest tank battle of the war, involving some 6,000 tanks, was the Battle of Kursk, which was fought on the Russian front in July, 1943. The battle, in which both sides suffered heavy losses, brought to an end Germany's last major offensive against the Russians.

One of the most spectacular uses of tanks in World War II was by General George S. Patton's Third Army following its breakthrough at St. L, France, on July 14, 1944. Patton's armored divisions led an advance of 400 miles (640 km), reaching the German border on September 12, but a lack of supplies forced a halt.

The U.S. Army had 16 armored divisions in World War II. Other armored units were mechanized cavalry groups and separate tank battalions. Antitank weapons developed during the war included the tank destroyer, bazooka, and recoilless rifle. (The tank destroyer, an armored vehicle carrying a heavy gun, was the forerunner of self-propelled artillery.)

Tanks played an important role in the early stages of the Korean War, but when the war became stalemated in mountainous terrain tanks were used mainly as fixed artillery. In the guerrilla fighting in Vietnam in the 1960's there was little opportunity for employment of armor in mass formations.

The first large use of tanks after the Korean War occurred during the Arab-Israeli wars of 1967 and 1973, when both sides committed hundreds of tanks to battle. In the 1973 conflict surface-to-surface antitank missiles carried by infantrymen destroyed large numbers of tanks, and some military experts declared that the tank was obsolete. Both the Arabs and the Israelis, however, continued to place value on the use of tanks and in the years after the war steadily increased their armored forces.

The principal development in the building of tanks during the 1960's and 1970's was the creation of the main battle tank (MBT), which was designed to replace both the medium tank and the heavy tank. It combines the speed of a medium tank with the armor and firepower of a heavy tank. MBT's include the Abrams (United States), AMX (France), Chieftain (Great Britain), Leopard (Germany), Morkava (Israel), and T-72 and T-80 (Russia).

During the 1980's, munition designers increased the penetrating power of antitank weapons, and tank designers responded by developing new forms of armor. The United States developed an extra-strength armor cast in flat slabs and, later, an armor made of a highly dense composite of steel and uranium. Israel and Russia both employed “reactive armor, basically a covering of explosives over the tank's armor plate; the explosives detonate when struck by a shell or missile, preventing it from penetrating.

In the Persian Gulf War (1991), the 100-hour land offensive that ended the war involved thousands of tanks, the largest number in a single operation since the Battle of Kursk in World War II.