Operation Hardtack II
Operation Hardtack II was a series of 37 nuclear tests conducted by the United States in 1958 at the Nevada Test Site. These tests followed the Operation Argus series and preceded the Operation Nougat series.
With test moratoriums on the horizon, American weapons labs rushed out many new designs. A hard deadline for testing was set at midnight, 31 October 1958, as negotiations were set to start that day, and the schedule shows it, with 29 tests executed in October, four of them on the last day. One other test was cancelled because weather delays postponed it across the midnight deadline. After the conclusion of Hardtack II, the United States announced a unilateral testing moratorium, which the Soviet Union joined after two last tests on 1 and 3 November. In September 1961, the Soviet Union resumed nuclear testing — including the test of the most powerful nuclear device ever designed, the Tsar Bomba, in October — and the United States followed suit with Operation Nougat.
Nuclear tests
Tamalpais
The Tamalpais test was conducted in the U12b.02 adit of Rainier Mesa by Lawrence Radiation Laboratory on October 8, 1958. The shot took place in a 394-foot-long hook-shaped drift ending in an unusually large test chamber lined with salt blocks as part of an experiment in preparation for Project Gnome. Additional experiments included measuring permanent tunnel displacement, seismic ground shock measurement, gas sampling by Oak Ridge National Laboratory, and electromagnetic pulse measurement by the Department of Defense Effects Test Group. The detonation of the.072 kiloton device released significant radioactive contamination and damage to the U12 tunnel complex, with radiation levels of 50R/h at the main portal and in the 10,000 R/h range in the tunnel immediately following detonation. The following day, workers reentered the tunnel and triggered a significant hydrogen gas explosion that further damaged the tunnel and injured three workers. Following the tunnel's evacuation, a second hydrogen explosion occurred later the same day.Adams
Adams was planned to be the final test of Hardtack II, but due to unfavorable winds the shot was never fired. The shot was intended to be a balloon test, and had been fully assembled and raised to firing altitude when it was cancelled. After midnight and the start of the moratorium, the device was lowered to the ground and disassembled. The Soviet Union would continue nuclear testing until 3 November.A 31 October 1958 meeting of the Atomic Energy Commission following the cancellation resulted in the following note: