Mark 7 Bomb
A SMaller, Lighter bomb
Explosive Power
18 to 61 kt.
Hiroshima Equivalent Factor
1.2x to 4x
Dimensions
15 feet x 30 inches
Weight
1600 lbs.
Year(s)
1952-1967
Purpose
Smaller, lighter bomb
About the Mark 7
In 1950, during the Korean War, we brought the B-29 Superfortress, the only plane we had capable of carrying the big Mark IV nuclear bomb, out of storage, moving them from Arizona where they had been mothballed to Guam, closer to North Korea. We also moved some to Great Britain, within range of Moscow itself. In this early Cold War example of nuclear saber-rattling, we were sending a message about our readiness to use atomic weapons not in response to any nuclear threat but instead a threat to use them to reverse our losses against conventional forces on a distant battlefield.
The fabled General Douglas MacArthur, commander of US forces in that war, knew that it was a bluff. The planes went to Guam and Great Britain (moves the enemy could see) and the Mark IVs went, too (which we assumed the enemy could figure out), but without their plutonium cores (which we hoped the enemy had great doubts about). MacArthur’s preference was not to bluff at all. He had no qualms about using the atomic bombs and he probably would have, citing his desire to end the war against the North Koreans and Chinese and to end it quickly, in a matter of days, by dropping thirty to fifty nuclear bombs—at a time when there were only about sixty such bombs in the entire inventory—on enemy airfields and supply depots all along the North Korean border with China and the USSR.
MacArthur did not drop the bombs as he wished since he did not have the legal authority to use the weapons (the President, after Nagasaki, imposed tighter controls over the permission to use atomic bombs and their targets) and he was also constrained at that time, odd as it might sound to modern ears, by the fact that the military did not have physical possession of the cores. For a few years, a civilian agency controlled them to prevent unauthorized use by military commanders.
One of MacAthur’s other ideas as part of his plan to win in Korea was to saturate the ground along the border, sea to sea some five miles in depth, with Cobalt 60, hoping to make the ground too radioactive for anyone to pass through.
In his own words, on his 74th birthday, three years after being unceremoniously relieved of command by President Truman, “For at least 60 years there could have been no land invasion of Korea from the North. The enemy could not have marched across that radiated collar I proposed to put across Korea’s neck.”
The AEC, founded in 1946, was something straight out of an Isaac Asimov novel, a civilian agency to keep the nukes out of the hands of the warmongering generals (maybe even out of the hands of the demagogic politicians). Scientists would be the rational actors, scientists would finally flex their power as the de facto arbiter of the world’s ultimate power. But in the real world, the military had direct control of nuclear weapons by 1951 and had control over the manufacturing of the weapons by 1954. The scientists could do the theoretical and design work but the bombs belonged to the military.
The Mark 7 was so much smaller, lighter, and far more aerodynamic than the earlier bombs of similar destructive power. It was able to be carried by fighter-bomber planes under one wing (though not at supersonic speeds) where it resembled a large fuel tank. It could be carried inside the big bombers, too, and it proved to be one of the most versatile, most desirable weapons in the rapidly expanding arsenal, used by all three services, and in the stockpile for 15 years, a long time for a nuclear weapon.
It was a successful bomb design and useful bomb. Such a useful bomb. They made sixteen to seventeen hundred of them.
Gallery
Nukemap
NUKEMAP is a web-based mapping program that attempts to give the user a sense of the destructive power of nuclear weapons. It was created by Alex Wellerstein, a historian specializing in nuclear weapons (see his book on nuclear secrecy and his blog on nuclear weapons). The screenshot below shows the NUKEMAP output for this particular weapon. Click on the map to customize settings.
Videos
Click on the Play button and then the Full screen button on the lower right (the brackets on a mobile device) to view each video. Click on the Exit full screen button (the “X” on a mobile device) to return.
Further Reading
- Wikipedia, GlobalSecurity.org, and Nuclear Compendium.
- The quote in the essay (above) comes from Bob Considine’s book, General Douglas MacArthur, published in 1964, as quoted in “Douglas MacArthur’s Plan to Win The Korean War” at Warfare History Network. Other information in the essay is drawn from “How the Korean War Almost Went Nuclear” by Carl A. Posey in the Smithsonian’s Air and Space Magazine.
- A New York Times article, published in 1964 indicated that the plan to use Cobalt 60 as a radioactive barrier in Korea was “said to have been supported by Drs. Ernest O. Lawrence, Edward Teller and others associated with atomic research at the University of California. It was seen as a way of ‘sanitizing’ a region without damage to property or loss of life.”
- The Mark 7 bomb was the one of first tactical nuclear weapons, intended to be carried by smaller, short-ranged aircraft and to attack targets nearer to friendly troops. The Council on Strategic Risks has a primer on what makes a weapon “tactical” (vs. “strategic”), offers a short history of tactical nuclear weapons, and includes interesting charts in the numbers and variety of weapons over time.
- “The Secret History of America’s Tactical Nukes,” by Jonathan Guyer, published in Vox in 2022, touches on the history of tactical nuclear weapons and makes the important point that the distinction between ‘tactical” and “strategic” nuclear weapons only came about much later with the negotiations of the arms control agreements.
- The 20th Fighter Wing, became, in 1951, the first unit to carry the Mark 7. “Victor Alert” by Rebecca Grant in Air Force Magazine, tells the story of the unit, soon stationed in Europe, and its role in US nuclear defense strategy.
- Robert F. Dunn (retired as Vice Admiral in the US Navy) recounts his time as a pilot in the 1950s learning the demanding (and, apparently, fun) lofting and over-the-shoulder maneuvers used to drop a Mark 7 in his article, “The Bomb and I,” published at the US Naval Institute. Here is a game simulation video of the maneuver and a video of a real airplane giving it a try.
- “The One-Way Nuclear Mission,” by John Lowery in Air Force Magazine in 2017 offers a clear graphic illustrating the toss-bomb technique with a Mark 7.
- The Mark 7 was tested in a live bomb drop in Nevada on November 1, 1951. The film, “Buster Jangle,” put out by the USAF Lookout Mountain Laboratory in Hollywood, documents (and recreates) this series of tests, of which Buster-Easy used the Mark 7 (start at 46:30 for the Buster-Easy portion of the film). Here is a fact sheet on Buster-Jangle by the Defense Threat Reduction Agency and another video angle on the detonation and yet another and still one more. Also, see the 1982 Defense Nuclear Agency’s history of the Buster-Jangle tests and the tests’ summary at the Nuclear Weapons Archive.
- The now unclassified “History of the Mk 7 Warhead” from August 1967 (collected in the Pfeiffer Nuclear Weapon and National Security Archive) is the Sandia National Lab’s own historical record of the Mark 7 and the other weapons in which its warhead version (the W-7) were used.
- There are far too many nuclear accidents and near accidents to go into detail here on American Nukes but note the list by Kelly M. in the comments to this post which cites an accident with a Mark 7.
- Want to build your own scale model of the Mark 7? You have several choices but the best I’ve found is an early version (1984) of Monogram’s kit #5432, which is a kit of the Republic Aviation F-84F Thunderstreak fighter-bomber–it comes with a Mark 7 as part of its optional armament.
- The warhead version of the Mark 7 was used in the Corporal missile, the Honest John rocket, the BOAR rocket (which also used the entire front of the Mark 7), and the Betty nuclear depth-charge. [Links to American Nukes forthcoming.]