Iran’s hardened, underground nuclear sites are impervious to most conventional weapons — except the U.S.-made 30,000-pound, deep-penetrating bomb.

The Air Force would have used it’s most powerful “bunker buster:” the 30,000-pound GBU-57 Massive Ordnance Penetrator. It is the most powerful bunker buster bomb in the U.S. Air Force’s arsenal, and was designed following the poor performance of bunker buster bombs employed during the 2003 invasion of Iraq.

MOP s were developed by America’s air force when it found that its existing bunker-busters could not damage Iraqi bunkers during the invasion in 2003. A new weapon had to be rushed into service. The MOP aimed to smash even deeper and harder bunkers being built in Iran and North Korea.