For some rockets and spacecraft the crew escape system was via an ejection seat, sometimes custom built for the task, sometimes adapted from an existing seat designed for a high performance plane.
Here's a great NASA paper on the Gemini ejection seat:
https://ntrs.nasa.gov/api/citations/19670019706/downloads/19670019706.pdf
For a more general overview this website has collected a lot of good information
http://www.ejectionsite.com/
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