Military aviators go through years of intense training to be able to fly worldwide aerial missions. Early training was conducted without the use of computers. In the early 1930s, the Link Flight Trainer was pioneered by Edwin Link, based on the vacuum technology that operated player pianos and organs. During World War II, over 10,000 trainers of this type were used to train more than 500,000 pilots. The Link Trainer has been designated as a Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers.