The T-12 also known as Cloudmaker demolition bomb was developed by the United States from 1944 to 1948. It was designed to attack targets invulnerable to conventional "soft" bombs, such as bunkers and viaducts. It achieved this by having an extremely thick nose section, which was designed to penetrate deeply into hardened concrete structures and then detonate inside the target after a short time delay. This created an "earthquake effect".
The T-12 was a further development of the concept initiated with the United Kingdom's Tallboy and Grand Slam weapons: a hardened, highly aerodynamic bomb of the greatest possible weight designed to be dropped from the highest possible altitude. Penetrating deeply in the earth before exploding, the resulting shock wave was transmitted through the earth into structures. The resulting camouflet could also undermine structures. The bomb could also be used against hardened targets. The T-12 was not a simple scale up of the M110, but incorporated modifications based on testing and calculations.
Originally set to meet a 42,000 lb (19,000 kg) target weight (the maximum payload for the experimental Convair B-36 "Peacemaker" bomber), the original design with its hardened case was slightly less than 43,000. The final T-12 weighed 43,600 lb (nearly 20 metric tons). This was twice the size of the United States' previous largest bomb, the Bomb, GP, 22,000-lb, M110 (T-14), the American-built version of the British Grand Slam. The B-36 was redesigned so it could carry the T12, although a converted B-29 Superfortress was used for testing.
Weapons of comparable size to the T-12, such as the BLU-82 and GBU-43/B Massive Ordnance Air Blast bombs (MOAB), were developed as latter-day United States superbombs, but their utility is limited outside the realm of psychological weapons and demolition. Only the GBU-43/B remains in the inventory. They are not hardened and lack the hard target capability of the T-12 and its cousins. The Massive Ordnance Penetrator has been recently developed in light of unsatisfactory penetration by existing 2000 lb and 5000 lb class weapons
