World War One took aviation from flights of hundreds of meters to flights measured in hundreds of kilometers. Early flight trainers were no more than barrels on ropes. Edward Link saw the potential for growth in aviation and the need for trained pilots to fly these more complex aircraft. The complexity of new planes would require a new level of fidelity in training systems, and the number of new pilots could not meet demand with current techniques.
This was brought to the forefront when 12 pilots were killed in training in less than three months. Link took his knowledge of building pump organs and created analog flight simulators designed to teach flight by instruments. There were no graphics of any kind and no scrolling landscapes, and the pilots were enclosed in a darkened covered cockpit. The trainers would respond accurately to the pilot's stick and rudder inputs and the little boxes would pitch and roll a few degrees. Link Trainers would add small stubby wings and a tail, making them look like the children's rides outside grocery stores in the 1950s, but over 500,000 pilots were trained with them.
For the Apollo program, true digital computers were used in simulators, but the computers were not powerful enough to display graphics. The computers displayed the simple analog readouts of the computers in the capsules. To simulate the view from the capsule, large three-dimensional models and paintings were built of the moon and space vehicles. The moon was scrolled under a Closed-Circuit TV Camera:
This was not unlike the scrolling panoramic paintings used a hundred years earlier. The video feed from the camera was sent to a special infinity optical display system mounted in the simulator capsule, which had a wide field of view of 110 degrees. As the astronaut trained in the simulator, the movement of his joystick was fed into the position of the cameras, changing the images projected in real time. This system featured wide field of view and interactivity, but not stereoscopic 3D images (though the life-sized cockpit model they looked through would add binocular depth to the presentation).