Operation Plumbob was a series of nuclear tests conducted by the United States government between May and October of 1957. Of these tests, one was the first nuclear explosion to be contained completely underground. This test was codenamed Rainier, and the device was detonated at a research facility in Nevada on this day in 1957.

The Rainier test

The nuclear bomb used in the Rainer test had a 1.7 kiloton yield, relatively small by today’s standards, but still an extremely dangerous bomb. The weapon was a modified version of America’s W-25 warhead, weighing roughly 220 pounds and measuring about 17 and a half inches in length and almost 26 inches in diameter.

The test was conducted at the Nevada Test Site (or NTS), a military testing site located north of Las Vegas. The Nevada Test Site has over a thousand miles of above-ground area for testing weapons in, but the Rainier test was conducted in a fully-enclosed tunnel beneath the research center. This made it the first nuclear weapon test that released no fission particles into the atmosphere. Seismologists around the world were able to detect the moment of the explosion using ordinary seismology tools.

The nuclear arms race

Rainier, and all the tests conducted during Operation Plumbob, took place during the Cold War period. At this time, the United States was engaged in a race with the Soviet Union to develop more effective nuclear weapons. Operation Plumbob was the longest and most controversial series of nuclear tests conducted by the United States, even to this day. Of the 29 explosions set off during the tests, only two did not produce a nuclear yield. The discoveries and refinements made during these tests contributed heavily to the development of nuclear warheads for intercontinental and intermediate-range missiles, as well as air defense and anti-submarine warheads.