. The Mk 21 nuclear gravity bomb was created in the United States, and was. Castle Romeo. Fireball Radius : 6. Calculates the effects of the detonation of a nuclear bomb. imported from Wikimedia project.  · But Biden’s defense budget threw a couple bones to the left: It aims to zero out funding for the cruise missile, known as the SLCM-N, and retire the B83 nuclear gravity bomb. Answer (1 of 3): There are a combined total of 100 B61-7 and B83 nuclear weapons in the active stockpile of the United States according to the Bulletin of the Atomic Scientists Nuclear Notebook. 2 megatons.