A tank is an armoured fighting vehicle designed for front-line combat, with heavy firepower, strong armour, tracks and a powerful engine providing good battlefield maneuverability. The first tanks were designed to overcome the deadlock of trench warfare in the 1910s; they are a mainstay of modern ground forces and a key part of combined arms combat. Modern tanks are versatile mobile land weapon system platforms, mounting a large-calibre cannon in a rotating gun turret, supplemented by mounted machine guns or other weapons. They combine this with heavy vehicle armour which provides protection for the crew, the vehicle's weapons, and its propulsion systems, and operational mobility, due to its use of tracks rather than wheels, which allows the tank to move over rugged terrain and adverse conditions such as mud, and be positioned on the battlefield in advantageous locations. These features enable the tank to perform well in a variety of intense combat situations, simultaneously both offensively with fire from their powerful tank gun, and defensively due to their near invulnerability to common firearms and good resistance to heavier weapons, all while maintaining the mobility needed to exploit changing tactical situations. Fully integrating tanks into modern military forces spawned a new era of combat, armoured warfare.
There are classes of tanks, some being larger and very heavily armored with high caliber guns, while others are smaller, lightly armored, and are equipped with a smaller caliber, lighter gun. These smaller tanks move over terrain with speed and agility and can perform a reconnaissance role in addition to engaging enemy targets. The smaller faster tank would not normally engage in battle with a larger, heavily armored tank, except during a surprise flanking maneuver.
The modern tank was the result of a century of development from the first primitive armoured vehicles, due to improvements in technology such as the internal combustion engine, which allowed the rapid movement of heavy armoured vehicles. As a result of these advances, tanks underwent tremendous shifts in capability in the years since their first appearance. Tanks in World War I were developed separately and simultaneously by Great Britain and France as a means to break the deadlock of trench warfare on the Western Front. The first British prototype, nicknamed Little Willie, was constructed at William Foster & Co. in Lincoln, England in 1915, with leading roles played by Major Walter Gordon Wilson who designed the gearbox and hull, and by William Tritton of William Foster and Co., who designed the track plates. This was a prototype of a new design that would become the British Army's Mark I tank, the first tank used in combat in September 1916 during the Battle of the Somme. The name "tank" was adopted by the British during the early stages of their development, as a security measure to conceal their purpose (see etymology). While the British and French built thousands of tanks in World War I, Germany was unconvinced of the tank's potential, and built only twenty.
Tanks of the interwar period evolved into the much larger and more powerful designs of World War II. Important new concepts of armoured warfare were developed; the Soviet Union launched the first mass tank/air attack at Khalkhin Gol (Nomonhan) in August 1939, and later developed the T-34, one of the predecessors of the main battle tank. Less than two weeks later, Germany began their large-scale armoured campaigns that would become known as blitzkrieg ("lightning war") – massed concentrations of tanks combined with motorised and mechanised infantry, artillery and air power designed to break through the enemy front and collapse enemy resistance.
The widespread introduction of high-explosive anti-tank warheads during the second half of World War II led to lightweight infantry-carried anti-tank weapons such as the Panzerfaust, which could destroy some types of tanks. Tanks in the Cold War were designed with these weapons in mind, and led to greatly improved armour types during the 1960s, especially composite armour. Improved engines, transmissions and suspensions allowed tanks of this period to grow larger. Aspects of gun technology changed significantly as well, with advances in shell design and aiming technology.
During the Cold War, the main battle tank concept arose and became a key component of modern armies. In the 21st century, with the increasing role of asymmetrical warfare and the end of the Cold War, that also contributed to the increase of cost-effective anti-tank rocket propelled grenades (RPGs) worldwide and its successors, the ability of tanks to operate independently has declined. Modern tanks are more frequently organized into combined arms units which involve the support of infantry, who may accompany the tanks in infantry fighting vehicles, and supported by reconnaissance or ground-attack aircraft.