John Paul Stapp, in 1954, sat in a rocket sled fired along rails in a series of steadily more violent tests. Speeds reached 631 mph, almost the speed of sound. This is a speed record for a manned rail vehicle that still stands today. At the end of the track the sled hit a trough of water that brought it to a rapid stop in around 1.4 seconds. In the most severe test, Stapp underwent an acceleration of 20 g as the rocket engine accelerated the vehicle up to speed and 46 g of deceleration (also a record) as the vehicle was brought to a stop. Stapp suffered numerous injuries in these tests (previous animal tests had shown that limbs could be broken merely by being pulled into the air stream), and several concussions. In the last test his eyes were bloodied as blood vessels burst in his eyes.