The Germans also started to develop a new series of heavy tanks. The first was the Tiger, which outclassed all its opponents in terms of firepower and armor when it was first put into operational use. The even heavier Tiger II (deemed "King Tiger" by Allied troops) supplemented the Tiger I late in the war. Its powerful gun - and unlike the Tiger I, its very heavy sloped armor - made it superior to nearly every Allied or Soviet tank in a one-on-one confrontation, but poor mobility, speed and reliability limited its use.