In the late 1940s and early 1950s, the military still had many questions concerning g-forces. In particular, it was not fully understood how many g-forces a person could handle, especially when ejecting from a plane. The belief was that nobody could live past 18 g. Colonel John Stapp, a USAF flight surgeon volunteered to undergo experiments involving extreme acceleration and deceleration. His most famous tests involved the use of a rocket sled which accelerated quickly and then came to a very sudden stop. In 1954 Sapp reached over 630mph on a rocket sled, decelerating to a stop in around one second. He had experienced 46 g, suffered a variety of injuries which including his eyes almost coming out of his head and eye bleeding, loss of sight and blisters on his body. Nonetheless, his work changed fighter aircraft design and the amount of protection given to pilots.