A tank is a large, heavily armoured vehicle with tracks and a large tank gun that is designed for front-line combat. Modern tanks are mobile land weapon platforms, mounting a large-calibre cannon in a rotating gun turret. 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 be positioned on the battlefield in advantageous locations. These features enable the tank to perform well in a tactical situation: the combination of powerful weapons fire from their tank gun and their ability to resist enemy fire means the tank can take hold of and control an area and prevent other enemy vehicles from advancing. In both offensive and defensive roles, they are powerful units able to perform key primary tasks[which?] required of armoured units on the battlefield. 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 during the World Wars of the 20th century.
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. Their first use in combat was by the British Army 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 French and British built thousands of tanks in WWI, 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 concepts of armoured warfare were developed; the Soviet Union launched the first mass tank/air attack at Khalkhin Gol (Nomonhan) in August 1939, which later resulted in the T-34, a predecessor 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 supported by motorised and mechanized 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 WWII 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 armours 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 Russian anti-tank weapons worldwide, the importance of tanks has waned. Modern tanks seldom operate alone, as they are organized into combined arms units which involve the support of infantry, who may accompany the tanks in infantry fighting vehicles. They are also usually supported by reconnaissance or ground-attack aircraft.
Main article: History of the tank
File:Tanks of WWI.ogg
Film clip of World War I-era tanks
The tank is the 20th century realization of an ancient concept: that of providing troops with mobile protection and firepower. The internal combustion engine, armour plate, and the continuous track were key innovations leading to the invention of the modern tank.
Armoured trains appeared in the mid-19th century, and various armoured steam- and petrol-engined vehicles were also proposed. The first armoured car was produced in Austria in 1904. However, all were restricted to rails or reasonably passable terrain. It was the development of a practical caterpillar track that provided the necessary independent, all-terrain mobility.
Many sources imply that Leonardo da Vinci and H.G. Wells in some way foresaw or "invented" the tank. Leonardo's late 15th century drawings of what some describe as a "tank" show a man-powered, wheeled vehicle with cannons all around it. However the human crew would not have enough power to move it over larger distance, and usage of animals was problematic in a space so confined.