A Tank is an armored vehicle that features a large caliber main gun generally inside a rotating turret. A tank moves via tracks/treads and usually has a secondary weapon to defend against infantry, either a coaxial MG or flamethrower. The tank was fielded by basically every country in World War II and saw extensive combat in every theater. The tank was first developed in WWI by the British and French to break the stalemate and actually advance through German lines. It received its name, the tank, to hide the fact that it was an armored fighting vehicle.
The Tank was first developed around 1915, although the Renaissance inventor Lenardo Da Vinci created the concept of the tank about 400 years earlier. The word "Tank" was meant to deceive spies by making them think the project was for a new water tanker, and whilst under development was covered under water reserviors, and for short "Tanks." The first tank used in combat was the Mark 1, used during the Battle of the Somme. Tanks have undergone many changes to them to counter the new anti-tank arms being produced. Increasing armour thickness was the most common form for obvious reasons and started in WW1 to help defend tank operators from armour pirecing rounds fired from machine guns. Increasing armour thickness also continued into World War II to counter the new explosive launching devices being used to counter them as well as other tanks. The idea of the turret was also implemeted in World War II as tanks used in WWI often housed simply an automatic weapon if any arms at all.