Qian Xuesen helped pioneer America’s early rocket program and later became a central figure in China’s missile and space programs. In between came one of the strangest episodes of the Cold War: the U.S. branded him a security risk, ordered him deported—then stopped him from leaving for five years because officials feared he knew too much.

This is the story of how America lost one of its most valuable scientists, a decision former Navy Secretary Dan Kimball later called “the stupidest thing this country ever did.”