The deep penetrating bombs that the US dropped into two Iranian nuclear facilities were designed specifically for those sites and were the result of more than 15 years of intelligence, the Pentagon said on Thursday. Gen Dan Caine, chairman of the Joint Chiefs of Staff Caine, the nation’s top military officer, offered new details about the work that went into building the “bunker-buster” bombs.

GBU bombs

The 30,000-pound GBU-57 A/B Massive Ordnance Penetrator bomb is comprised of steel, explosive and a fuse programmed to a specific detonation time. Over the years, the military tested and retested it hundreds of times on mock facilities.