[chris]

The Atlas D testing program began on April 14, 1959, with the launch of Missile 3D from Launch Complex 13.

Engine startup was normal, but the LOX fill/drain valve did not close properly, spilling liquid oxygen around the thrust section. The RP-1 fill/drain valve then leaked, allowing the propellants to mix and explode on the launch stand.

The open LOX valve also caused a loss of fuel flow and pressure, leaving the B-2 engine at 65 percent thrust. The unbalanced thrust sent the Atlas upward at a slanted angle and prevented one launcher hold-down arm from retracting properly.