In World War I, army tanks were not equipped with turrets until the French light tank known as the FT-17 was developed. Though the French tank only had a machine gun as its primary weapon, it set the path for the designs of modern army tanks. Compared to tanks used in the early days of  world of tanks  power leveling  , tanks that were used in World War I were relatively large. By the time World War II started, a number of army tanks were equipped with a 37mm cannon. World War II was the time when army tanks increased in size; there were even the 50 ton Tiger tanks. This meant that larger sized tanks could carry larger weapons. During the time of World War II, the Soviets' army tanks had the biggest production tank gun; this was the IS-2 tank with a 122mm cannon. The IS-2 tank was the Soviets way of responding to the Germans Tiger and King Tiger army tanks, which were equipped with an 88mm cannon. The M-26 Pershing was built by the United States, and it has a 90mm cannon. During World War II, armor was primarily made from steel; however, after World War II when SABOT rounds and guided missiles were developed, new types of armor were also made. Because of the development of new armor, bigger main guns army tanks got smaller. A tank was harder to hit the closer to the ground it was. Since they would sink in Vietnam's rice paddies, the United States primarily used their army tanks as mobile artillery. North Vietnam made use of the T-55 and the T-34 tanks. When the U. S. invaded Vietnam in 1972, many of North Vietnam's Soviet built army tanks were destroyed by U. S. helicopters that were armed with guided missiles. In the 1960s and 1970s, in order to enhance their fighting abilities, army tanks were equipped with night vision, laser sights and other improvements. In order to decimate missiles and shaped charge rounds, explosive armor was developed by the Israelis. Researches done by the Americans and the British revealed that the armor was based on exhausted uranium. Smooth bore guns have now been added to modern army tanks. For about the same weight, smooth bore guns can fire a large shell just like the rifled tubes of older army tanks, and they also last longer. The Original M-1 used a 105mm main gun, while the German Leopard 2 and the M1A3 uses a 120mm main gun. Army tanks that are used in modern times are now equipped with wireless networking that can be used to communicate with air support aircrafts, command posts, artillery, other army tanks and helicopters.