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Ivy Mike Nuclear Test

... was the first thermonuclear device built upon the Teller-Ulam principles of staged radiation implosion. The device was designed by the Panda Committee directed by J. Carson Mark at Los Alamos (Edward Teller declined to play a role in its development). The enormous explosion was

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the 4th largest device ever tested by the U.S.  The island the test device was installed on, Elugelab (code named Flora), was entirely destroyed. The resulting crater was 6240 ft across and 164 ft deep. High levels of radiation blanketed much of the atoll following the test.

Test: Time: Location: Test Height: Yield:
Mike
19:14:59.4 31 October 1952 (GMT) 
07:14:59.4 1 November 1952 (local)
Elugelab ("Flora") Island, Enewetak Atoll
Surface burst
10.4 Mt

Mike was a "two stage" device and had a yield of 10.4 megatons.  The primary stage was a TX-5 fission bomb, the secondary stage consisted of liquid deuterium fusion fuel stored in a cylindrical Dewar (thermos) flask. Running down the center of the Dewar was a plutonium "spark plug" rod to ignite the fusion reaction. The Dewar was surrounded by a natural uranium pusher/tamper weighing more than 5 metric tons. The entire assembly was housed in an enormous steel casing, 80 inches wide and 244 inches long, with walls ~10-12 inches thick, the largest single forging made up to that time. The inside surface of the casing was lined with sheets of lead and polyethylene to form the radiation channel that conducted heat from the primary to the secondary. The entire device weighed 82 tons.

It is part of my responsibility as Commander in Chief of the Armed forces to see to it that our country is able to defend itself against any possible aggressor. Accordingly, I have directed the AEC to continue its work on all forms of atomic weapons, including the so-called hydrogen or Super bomb.

-- President Harry S. Truman, 31 January 1950

On 31 January 1950 Pres. Harry S. Truman publicly declared the U.S. intention to develop a hydrogen bomb. The primary motivations for this declaration was were two surprising revelations - the Soviet Union's first fission bomb during the previous fall; and the discovery of Klaus Fuchs' espionage activity of at Los Alamos, uncovered just days before. These combined shocks, added to the rapidly growing Cold War tensions, created grave concern at the highest levels of Washington about the United States being overtaken in a nuclear arms race by the Soviet Union.

From that time onward, the highest priority was placed on developing new and more potent strategic weapons - especially thermonuclear weapons (hydrogen bombs). At that time though no one had good ideas about how a practical thermonuclear weapon could be made, rendering Truman's declaration hollow. This raised new fears - that Truman's pronouncement may have spurred Soviet thermonuclear efforts onward even faster, and that they might have hit upon concepts not yet known in the U.S. Consequently a fallback strategy was pursued - developing the highest yield fission bomb possible, a technical effort lead by Theodore Taylor at Los Alamos. The conceptual breakthroughs of Stanslaw Ulam and Edward Teller the following January provided the needed insights to develop a thermonuclear device.

So from early 1951 onward, these two parallel efforts to develop high yield weapons were focused on a Pacific Proving Ground of test series for late in 1952. This series - Operation Ivy - exploded the two largest bombs tested up to that time. It inaugurated the thermonuclear age with the first "true" thermonuclear test (code name Mike), which was considerably more powerful than all the high explosives used in two World Wars put together. Ivy also tested the highest yield pure fission weapon ever exploded.