Apollo 1, also known as AS-204, was the first manned mission of the United States Apollo program. It was intended to be the first manned flight of the Apollo spacecraft, which was designed to land astronauts on the Moon. The mission was scheduled to launch on February 21, 1967, but a fire broke out in the spacecraft during a pre-launch test on January 27, killing all three astronauts on board: Gus Grissom, Edward White, and Roger Chaffee.
The fire was caused by a spark from an electrical wire that ignited a fire in the pure oxygen-rich environment inside the spacecraft. The astronauts were unable to escape due to the lack of a hatch that could be opened from the inside.
The disaster led to significant changes in the design and testing of the Apollo spacecraft, and the next manned mission, Apollo 7, did not launch until October 1968.