Program 437

Program 437 was the second anti-satellite weapons program of the U.S. military. The US anti-satellite weapons program began development in the early 1960s and was officially discontinued on 1 April 1975. Program 437 was approved for development by U.S. Secretary of Defense Robert McNamara on November 20, 1962, after a series of tests involving high altitude nuclear explosions. The program's facilities were located on Johnston Island, an isolated island in the north central Pacific Ocean.

The US's first anti-satellite system was Program 505, based at the Kwajalein Missile Range, about halfway between Hawaii and the Philippine islands. This system became operation in 1962, based on the Nike Zeus anti-ballistic missile that had been tested at that site. These missiles had been modified for greater range, but even with these modifications the system could only intercept satellites that flew very close to the base, with a maximum altitude around 150 nautical miles (280 km; 170 mi). A system with longer range was an obvious requirement.

Program 437 was based on the much more powerful PGM-17 Thor ballistic missile. It used Thor DSV-2E missiles armed with a W49 or W50 nuclear weapon, which would destroy or disable targets through nuclear explosion or the resulting electromagnetic pulse. Eight Thor DSV-2E missiles were launched between May 2, 1962 and November 1, 1962. Though the program would routinely run successful tests with unarmed Thor missiles, the only high altitude nuclear explosions were conducted through Operations Argus, Hardtack I, and Dominic/Fishbowl between 1958-1962. Operation Argus operated out of the South Atlantic, while Hardtack and Dominic conducted their high altitude tests from the Johnston Island facilities. "Tightrope" was part of "Fishbowl" but was a lower altitude detonation.

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