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Operation Ivy


Operation Ivy

Operation Ivy
Ivy Mike
Country United States
Test site Elugelab (Flora), Enewetak Atoll; Runit (Yvonne), Enewetak Atoll
Period 1952
Number of tests 2
Test type dry surface, free air drop
Max. yield 10.4 megatonnes of TNT (44 PJ)
Previous test series Operation Tumbler–Snapper
Next test series Operation Upshot–Knothole

Operation Ivy was the eighth series of American nuclear tests, coming after Tumbler-Snapper and before Upshot-Knothole. Its purpose was to help upgrade the U.S. arsenal of nuclear weapons in response to the Soviet nuclear weapons program. The two explosions were staged in late 1952 at Eniwetok Atoll in the Pacific Proving Ground in the Marshall Islands.


  • Tests 1
    • Mike 1.1
    • King 1.2
  • Summary 2
  • References 3
  • External links 4



The first Ivy shot, Mike, was the first successful full-scale test of a multi-megaton thermonuclear weapon ("hydrogen bomb") using the Teller-Ulam design. Unlike later thermonuclear weapons, Mike used deuterium as its fusion fuel, maintained as a liquid by an expensive and cumbersome cryogenic system. It was detonated on Elugelab Island yielding 10.4 megatons, almost 500 times the yield of the bomb dropped on Nagasaki. Eight megatons of the yield was from fast fission of the uranium tamper, creating massive amounts of radioactive fallout. The detonation left an underwater crater 6,240 ft (1.9 km) wide and 164 ft (50 m) deep where Elugelab Island had been. Following this successful test, the Mike design was weaponized as the EC-16, but it was quickly abandoned for solid-fueled designs after the success of the Castle Bravo shot.

Jimmy Priestly Robinson, age 28,[1][2] a USAF captain, was lost near the end of his mission to successfully pilot his F-84G through the mushroom cloud's stem to collect radiochemical air samples. After re-emerging from the cloud, both he and his wingman Red 3 pilot Captain Bob Hagan, encountered difficulties picking up rendezvous and runway navigational beacons due to "electromagnetic after effects" of the detonation.[3] By the time they were successful in finding the signal they were dangerously low on fuel, and before reaching the runway both had depleted their reserves. While Hagan was able to glide to the runway and achieve a hard landing, Robinson was instead too far out to follow the same path and therefore attempted to land on water,[3] but was never found.[2]

Approximately a year after his disappearance, Robinson was awarded a posthumous Distinguished Flying Cross for his service.[3] Neither his plane nor his body has ever been found, in 2002 a memorial stone at Virginia’s Arlington National Cemetery was erected.[2] The manned cloud sampling practice had a long history of success, with Robinson being one of a total of four pilots who sampled the Mike cloud stem on that day, all of which were led by their flight leader Lieutenant Colonel Virgil Meroney, who was part of the nascent 1211th Test Squadron.[3]


The second test, King, fired the largest nuclear weapon to date using only nuclear fission (no fusion nor fusion boosting). This "Super Oralloy Bomb" was intended as a backup if the fusion weapon failed. King yielded 500 kilotons, 25 times more powerful than the Fat Man weapon.


United States' Ivy series tests and detonations
Name [note 1] Date time (UT) Local time zone [note 2][4] Location [note 3] Elevation + height [note 4] Delivery,[note 5]
Purpose [note 6]
Device [note 7] Yield [note 8] Fallout [note 9] References Notes
Mike 31 October 1952 19:14:59.4 MHT (11 hrs)
Elugelab (Flora), Enewetak Atoll 2 m (6 ft 7 in) + 8 m (26 ft) dry surface,
weapons development
TX-5 primary "Sausage" 10.4 Mt [5][6][7][8] Megaton device. First true experimental H-bomb, used cryogenic deuterium; became TX-16 weapon. Elugelab completely cratered.
King 15 November 1952 23:30:00.0 MHT (11 hrs)
Runit (Yvonne), Enewetak Atoll 0 + 450 m (1,480 ft) free air drop,
weapons development
Mk-18F SOB 500 kt [5][6][7][8] Kiloton device. Aka Super oralloy bomb (SOB), used 4 critical masses of U235. Largest pure fission device; also tested chain safety device.
  1. ^ The US, France and Great Britain have code-named their test events, while the USSR and China did not, and therefore have only test numbers (with some exceptions – Soviet peaceful explosions were named). Word translations into English in parentheses unless the name is a proper noun. A dash followed by a number indicates a member of a salvo event. The US also sometimes named the individual explosions in such a salvo test, which results in "name1 – 1(with name2)". If test is canceled or aborted, then the row data like date and location discloses the intended plans, where known.
  2. ^ To convert the UT time into standard local, add the number of hours in parentheses to the UT time; for local daylight saving time, add one additional hour. If the result is earlier than 00:00, add 24 hours and subtract 1 from the day; if it is 24:00 or later, subtract 24 hours and add 1 to the day. All historical timezone data (excepting Johnston Atoll) are derived from here:
  3. ^ Rough place name and a latitude/longitude reference; for rocket-carried tests, the launch location is specified before the detonation location, if known. Some locations are extremely accurate; others (like airdrops and space blasts) may be quite inaccurate. "~" indicates a likely pro-forma rough location, shared with other tests in that same area.
  4. ^ Elevation is the ground level at the point directly below the explosion relative to sea level; height is the additional distance added or subtracted by tower, balloon, shaft, tunnel, air drop or other contrivance. For rocket bursts the ground level is "N/A". In some cases it is not clear if the height is absolute or relative to ground, for example, Plumbbob/John. No number or units indicates the value is unknown, while "0" means zero. Sorting on this column is by elevation and height added together.
  5. ^ Atmospheric, airdrop, balloon, gun, cruise missile, rocket, surface, tower, and barge are all disallowed by the Partial Nuclear Test Ban Treaty. Sealed shaft and tunnel are underground, and remained useful under the PTBT. Intentional cratering tests are borderline; they occurred under the treaty, were sometimes protested, and generally overlooked if the test was declared to be a peaceful use.
  6. ^ Include weapons development, weapon effects, safety test, transport safety test, war, science, joint verification and industrial/peaceful, which may be further broken down.
  7. ^ Designations for test items where known, "?" indicates some uncertainty about the preceding value, nicknames for particular devices in quotes. This category of information is often not officially disclosed.
  8. ^ Estimated energy yield in tons, kilotons, and megatons. A ton of TNT equivalent is defined as 4.184 gigajoules (1 gigacalorie).
  9. ^ Radioactive emission to the atmosphere aside from prompt neutrons, where known. The measured species is only iodine-131 if mentioned, otherwise it is all species. No entry means unknown, probably none if underground and "all" if not; otherwise notation for whether measured on the site only or off the site, where known, and the measured amount of radioactivity released.


  1. ^
  2. ^ a b c
  3. ^ a b c d
  4. ^
  5. ^ a b
  6. ^ a b
  7. ^ a b
  8. ^ a b

External links

  • Curtiss Atomic Marines
  • Operation Ivy
  • Analysis of Radiation Exposure for Navy Personnel at Operation Ivy
  • The short film Operation IVY is available for free download at the Internet Archive formerly classified
  • The short film Operation Ivy (1952) is available for free download at the Internet Archive formerly unclassified, for civil defense
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