It was 1965, and the Pentagon and CIA were worried. The Vietnam War was beginning to ramp up. The People’s Republic of China had recently conducted its first nuclear test, but intelligence was limited. Chinese missile tests were being conducted at a secretive facility a few hundred miles north of the Himalayan mountains, but intelligence estimates for the missiles’ range — and compatibility with nuclear warheads — was unclear. The mountain range blocked ground-based sensors, which could have picked up the missiles’ radio telemetry signals. Worse, Pakistan had just kicked out America’s spy planes, and precision satellite imagery was still primitive.