Fifty years ago today, the three-man crew of the Apollo 1 mission were killed when a fire broke out inside their Command Module during a launch rehearsal test at Cape Canaveral (then named Cape Kennedy Air Force Station), Launch Complex 34, on January 27, 1967. The astronauts were unable to open the hatch from inside.
The Apollo 1 crew members were (pictured above left to right)
U.S.A.F. Lt. Colonel Virgil I. "Gus" Grissom
U.S.A.F. Lt. Colonel Edward H. White, II
U.S.N. Lt. Commander Roger B. Chaffee
Apollo 1 would have been Chaffee's first space flight, White's second, and Grissom's third.
The Command Module had been mated to (connected atop of) the towering Saturn IB launch vehicle on January 6. The scheduled launch date was February 21, and the January 27 test was a crucial one to see if the spacecraft would operate with internal electrical power.
A description of the moments of the fire is available on the Apollo 1 Wikipedia page; my summary chronology is below.
6:31:04.7 EST, Grissom exclaims
c. 6:31:06.2 EST, Chaffee reports fire
c. 6:31:13 EST, start of final, garbled transmission, perhaps White, 5.0 sec. long
6:31:19 EST, intense cabin pressure ruptures Command Module's inner wall
The review board determined that there had been a momentary power failure at 6:30:55 EST, but a single ignition source was never identified. (See full report.)
The launch complex was used for a final time on October 11, 1968—for the first manned Apollo launch, that of Apollo 7—and later decommissioned. NASA razed most of it, but the launch pedestal remains. A memorial plaque is affixed to it.
Image: NASA photograph of January 17, 1967; photographer unknown.