Training simulations have been used by various industries including the military, entertainment, aviation, and medicine. Aviation was the leading industry of modern simulators. In 1929, Edwin Link developed the first Link Trainer, or the “Blue Box”, for aviation training. The Link Trainer had a cockpit, controls, and motions simulating that of a real airplane. In 1934 pilots used the Link Trainer for flight simulations after twelve Army Air Corp pilots were killed in fewer than 3 months trying to deliver air mail. Army Air Corp bought six Link Trainers in order for pilots to become familiar with airplane controls and flying conditions. The Link Trainers gained popularity during World War II, when more than 10,000 Trainers were sold to combatant nations. Blue Boxes trained more than 500,000 US pilots. Today, flight simulators with advanced software and computer screens have become required components in aviation pilot training in the US.