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The mushroom cloud from the Mike shot.

Ivy Mike was the code name given to the first successful test of a fusion device, detonated on October 31, 1952 (US time — November 1 local time) by the United States on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy. The device was the first full test of the Teller-Ulam design for a "staged" fusion bomb.

Due to its physical size and fusion fuel type (cryogenic liquid deuterium) the Mike device was not itself suitable for use as a thermonuclear weapon. A simplified and lightened bomb version (the EC-16) was prepared, and scheduled to be tested in Castle Yankee, as a backup in case the non-cryogenic "Shrimp" fusion device (tested in Castle Bravo) failed to work; that test was cancelled when the Bravo device was successful.

A view of the Sausage device casing, with its diagnostic and cryogenic equipment attached. The long pipes would receive the first bits of radiation from the primary and secondary ("Teller light") just as the device was detonated. Note man seated lower right for scale.

The "Mike" device was essentially a very large cylindrical thermos flask for holding the cryogenic deuterium fusion fuel, with a regular fission bomb (the "primary") at one end; the latter was used to create the conditions needed to start the fusion reaction.

The primary stage was a TX-5 boosted fission bomb in a separate space atop the assembly (so it would not freeze, rendering it inoperable). The "secondary" fusion stage used liquid deuterium despite the difficulty of handling this material, because this fuel simplified the experiment, and made the results easier to analyze. Running down the center of the flask which held it was a cylindrical rod of plutonium (the "sparkplug") to ignite the fusion reaction. Surrounding this assembly was a five-ton natural uranium "tamper". The interior of the tamper was lined with sheets of lead and polyethylene foam, which formed a radiation channel to conduct X-rays from the primary to secondary. (The function of X-rays was to hydrodynamically compress the secondary, increasing the density and temperature of the deuterium to the levels needed to sustain the thermonuclear reaction, and compressing the sparkplug to supercriticality ignition.) The outermost layer was a steel casing 10-12 inches thick. The entire "Sausage" (as it was nicknamed) assembly measured 80 inches in diameter and 244 inches in height and weighed about 60 tons.

The entire Mike device (including cryogenic equipment) weighed 82 tons, and was housed in a large corrugated-aluminium building called a "shot cab" which was set up on the Pacific island of Elugelab, part of the Enewetak atoll.

A 9,000-foot long artificial causeway connected the islands of Elugelab, Teiter, Bogairikk, and Bogon. Atop this causeway was an aluminium-sheathed plywood tube (named a "Krause-Ogle box") filled with helium ballonets. This allowed gamma and neutron radiation to pass uninhibited to an unmanned detection station housed in a bunker on Bogon.

In total, 9,350 military and 2,300 civilian personnel were involved in the Mike shot. A large cryogenics plant was installed on Parry Island, at the South end of the Eniwetak atoll, to produce the liquid hydrogen (used for cooling the device) and deuterium needed for the test.

Enewetak Atoll, before Mike shot. Note island of Elugelab on left.

Enewetak Atoll, after Mike shot. Note crater on left.

The test was carried out 0715 hours local time on November 1, 1952; it produced a yield of 10.4 megatons (10.4 million tons of TNT). However, 77% of the final yield came from fast fission of the uranium tamper, which meant that the device produced large amounts of fallout.

The fireball was over 3 miles wide, and the mushroom cloud rose to an altitude of 57,000 feet in less than 90 seconds. One minute later it had reached 108,000 feet, before stabilizing at 120,000 feet, with the top eventually spreading out to a diameter of 100 miles (the stem was 20 miles wide).

The blast created a crater 6,240 feet in diameter and 164 feet deep where Elugelab had once stood; the blast and water waves from the explosion (some waves up to twenty feet high) stripped the test islands clean of vegetation, as observed by a helicopter survey within 60 minutes after the test, by which time the mushroom cloud and steam had been blown away. Irradiated coral debris fell upon ships stationed 30 miles from the blast, and the immediate area around the atoll was heavily contaminated for some time.

The entire shot was documented by the filmmakers at Lookout Mountain. The film was accompanied by powerful, Wagner-esque music featured on many test films of that period and was hosted by actor Reed Hadley. After the test a private screening was given to President Dwight D. Eisenhower. It was later released to the public after sanitizing, and was for many days played continually on many television channels.

Edward Teller, who was perhaps the most ardent supporter of the development of the hydrogen bomb, was in Berkeley, California at the time of the shot. He was able to receive first notice that the test was successful by observing a seismometer, which picked up the shock wave travelling through the earth all the way from the South Pacific test site.^[1]

• History of nuclear weapons
• Ivy King
• Operation Castle

Wikimedia Commons has media related to:

Operation Ivy

• Downloadable/Streamable Declassified Film: Operation IVY (1 hour originally Secret version, 1953) at the Internet Archive
• Operation Ivy film (27 minutes unclassified civil defence version, 1953)
• Operation Ivy

• Chuck Hansen, U. S. Nuclear Weapons: The Secret History (Arlington: AeroFax, 1988)
• Richard Rhodes, Dark Sun: The Making of the Hydrogen Bomb (New York: Simon and Schuster, 1995)

Coordinates: 11°40′0″N, 162°11′13″E