The T-12 (also known as Cloudmaker) earthquake bomb was developed by the United States from 1944 to 1948 and deployed until the withdrawal of the Convair B-36 Peacemaker bomber aircraft in 1958. It was one of a small class of bombs designed to attack targets invulnerable to conventional "soft" bombs, such as bunkers and viaducts. It achieved this by having an extremely thick, hardened nose section designed to penetrate deeply into hardened concrete structures and then detonate inside the target after a short time delay.