Nuclear Bomb Still off Georgia’s coast

The ‘Mark 15, Mod 0’ nuclear bomb was jettisoned into the Atlantic Ocean off Savannah after a B-47 bomber and an F-86 fighter collided in mid-air. ‘The 7,600-pound, 12-foot-long thermonuclear bomb contained 400 pounds of high explosives as well as uranium’ and it was found off Tybee Island by retired Air Force Lt. Colonel Derek Duke.

This was a transitional device between the earliest, liquid-dueterium monsters and modern three-stage designs. They weren’t yet sure how to achieve efficient compression of the fusion stage, so they wrapped the bomb in highly-enriched uranium to be sure the fusion stage would light off. The bomb had a design yield of 1.7 megatons, and something like 1.3 megatons of that would be due to the fission of the U-235 jacket.

That means that this bomb contains a lot of weapons grade uranium. Again, 1.3 megatons of yield from the fission of uranium. The largest pure-fission bomb we ever detonated was the 500-kiloton Mark 18 prototype, and that used about 60 kilograms of HEU. Assuming linear scaling, that means we’re looking at upwards of 156 kilograms of HEU in this bomb. Critical mass of uranium’s about 16 kilograms. Double that to overengineer a bomb, and that means whoever gets their mitts on this thing could build 4 or 5 crude Hiroshima-type bombs, each with a yield of several kilotons.

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