Tank, heavily armoured track-laying, or treaded, military vehicle, with cross-country mobility and road speeds up to 97 km/h (60 mph). Tanks are classified as light, medium, and heavy. They range in weight from approximately 14 to 54 metric tons, have at least 15 cm (6 in) of armour plate, and mount cannons ranging from 75 mm to 122 mm in the tank's turret. The turret is a structure on top of the tank that can rotate 360 degrees, enabling the tank to fire in any direction. In addition, tanks often have both light and heavy machine-guns. Light tanks are used for reconnaissance; heavier tanks are used primarily to penetrate or flank enemy defences.
The concept of armour protection dates from antiquity. By the 5th century BC Greek warriors, and sometimes their horses, wore armour. Florentine artist and scientist Leonardo da Vinci designed a crank-operated covered chariot in 1482, but development of an effective, track-laying armoured vehicle was only possible after the invention of the internal-combustion engine.
During World War I Britain developed and used the first armoured track-laying vehicles. To maintain secrecy, the vehicles were shipped to the battle zone in crates marked "tanks", hence the origin of the name. The first battle in which these tanks were employed was the Battle of the Somme, on September 15, 1916, when Britain used 49 tanks with disappointing results. Little more than a year later, however, in November 1917, 400 British tanks penetrated German lines near Cambrai, capturing 8,000 enemy soldiers and 100 guns.
Tanks played an even greater role in warfare during World War II. Early in the war Germany organized tanks, infantry, artillery, and support troops into fast, mobile attack units; these units were responsible for many of Germany's early victories in the war. As a result the nations opposing Germany in the war quickly incorporated tanks into their military forces. By the middle of the war, tanks were a central part of most infantry units, and played a prominent role in battles in the Union of Soviet Socialist Republics (USSR) in the deserts of northern Africa, and in Europe.
Tanks continue to be an important part of military forces and have played an important role in many wars, such as the Yom Kippur War (1973) and the Gulf War (1991). Modern tanks do not differ substantially from tanks used towards the end of World War II, but are better armoured, faster, and use more powerful cannons.
In addition, computer firing controls enable modern tanks, such as the British Challenger, the German Leopard I and II, the M1 Abrams tank of the United States military, and the former Soviet T-series, to accurately fire on targets even while moving.