Operation Hardtack I
1958 - Pacific Proving Grounds
Hardtack I included 35 tests, the largest test series so far (1958 in fact saw a total of 77 U.S. tests, more than the three previous record setting years combined). Partly this burst of testing activity was due to building pressure for an imminent test moratorium, leading the weapons labs to rush as many device types to the test range as possible. A total of 35.6 megatons were shot during this series.
The lab tests centered on ICBM and SLBM missile warheads and high yield strategic bombs. The DOD conducted high altitude multi-megaton tests to study their usefulness for ABM (anti-ballistic missile) warheads, and discovered the high-altitude EMP (electromagnetic pulse) effect in the process. Effects tests of underwater explosions were also conducted.
The extensive test schedule required the use not only of both atolls (Bikini and Enewetak) but Johnston Island also. This series was the last to conduct atmospheric testing at Bikini and Enewetak atolls. Test names were taken from North American trees and shrubs.