The two-seat Gemini capsule, unlike the Mercury and Apollo and their rocket-powered escape towers, employed ejection seats to allow the astronauts to escape in an emergency. Made by Weber Aircraft, those ejection seats had to function from the launch pad (zero velocity) up to 40,000ft. at high Mach number.
A boilerplate Gemini during a simulated pad-abort test. The open doors were important.
It could have been even more startling.