U.S. may have only a low-single-digit number of GBU-57 bombs after using 14 against Iran’s Fordow and Natanz facilities, with replacements taking years

A new analysis by CSIS estimates that the U.S. military has only a low-single-digit number of its GBU-57 bunker-busting bombs remaining as Iran continues expanding deeply buried military and nuclear facilities.

The United States used 14 of the 30,000-pound bombs against Iran’s Fordow and Natanz nuclear facilities in June 2025. The Pentagon has allocated $123 million to replenish the stock, but replacements could take several years to arrive, the analysis says.

The report also estimates that about 10 GBU-43/B Massive Ordnance Air Blast bombs, commonly known as the “Mother of All Bombs,” remain in the U.S. inventory. Trump is reportedly considering using them in further strikes against Iran, although they are less effective against deeply buried targets than the GBU-57.