Heavily armed and armoured combat vehicle that moves on two continuous metal chains called tracks. It is usually equipped with a cannon mounted in a revolving turret as well as lighter automatic weapons. The British developed tanks during World War I to fill the need for an armoured assault vehicle that could cross the muddy, uneven terrain of the trench battle zone. They first saw combat at the Battle of the Somme (1916). In World War II, Germany's tank force was initially the most effective in Europe because it was organized into fast-moving massed formations with great striking power. After World War II, tanks became larger and more heavily armed. Most modern main battle tanks weigh more than 50 tons yet are capable of road speeds of 30–40 mph (50–70 kph). The standard main armament is a 120-mm gun, which fires armour-piercing projectiles; laser range-finders and infrared imaging devices aid in sighting.