17 August 1946 – The first person in the U. S. to be ejected from an airplane (P-61) by means of its emergency escape equipment was Sergeant Lambert at Wright Field in Ohio. (1) 
“Sergeant Larry Lambert ejected from an airplane while in flight over Wright Field. Lambert was testing a new device to assist pilots in escaping from high-speed aircraft. The test was successful, making Lambert the first man to eject from an aircraft while in flight and to do so successfully.” (2)
The ejection took place with the “aid of the newly developed Material Air Command’s pilot ejection seat. Lambert was shot out of the seat at an altitude of 6,000 feet.” (3)
Sources: (1) Wikipedia/Portal:Aviation; (2) ohiohistorycentral.org; (3) Ejection Seat Test (508pir.org)