 Safeguard C was the basis for maintaining Johnston Atoll as a "ready to test" above-ground nuclear testing site should atmospheric nuclear testing ever be deemed to be necessary again.In 1993, Congress appropriated no funds for the Johnston Atoll "Safeguard C" mission, bringing it to an end.Program 437 turned the PGM-17 Thor into an operational anti-satellite (ASAT) weapon system, a capability that was kept top secret even after it was deployed.