The Department of War is running low on a critical munition as President Donald Trump weighs next steps in Iran, according to an Oct. 15 report.

The supply of so-called “bunker busters,” a class of weapons used to destroy what the Department of War characterizes as “hard and deeply buried targets” (HDBT), are dwindling as Iran digs deeper underground to avoid conventional American weaponry, according to a Center for Strategic and International Studies (CSIS) report penned by Defense and Security Department Senior Adviser and Retired Marine Col. Mark Cancian and research associate Chris Park.

The Pentagon did not immediately respond to a Daily Caller News Foundation request for comment.

“The U.S. needs bunker busters that can address two target sets. One is the large number of tunnels and other moderately difficult targets, which require volume. The other is a much smaller but more difficult target set of facilities inside mountains,” write @MarkCancian and…

— CSIS (@CSIS) October 17, 2026

Bunker busters are primarily air-dropped bombs that can be fit with laser or GPS guidance kits to be configured as guided bomb units (GBUs). In contrast to conventional bombs — though they can also be nuclear weapons — bunker busters feature significantly heavier casing and smaller explosive charges. In addition, versions of existing standing munitions were re-designed with deeper penetrating systems during the wars in Iraq and Afghanistan; some are counted among the current stockpile.

The 30,000 pound Massive Ordnance Penetrator (MOP) is one of the most recognized bunker-busting bombs. A total of “14 MOPs were used in the attacks on Iran’s nuclear facilities at Fordow and Natanz during Operation Midnight Hammer,” according to CSIS. “The number of MOPs remaining in the U.S. inventory is estimated to be in the low single digits.”

The demand for bunker busters will only increase as “Iran and other adversaries dig deeper into mountains to put high-value military facilities beyond the reach of conventional weapons.” These “high-value military facilities” include 33 underground Iranian missile bases near the Strait of Hormuz that survived earlier military attacks, according to CSIS.

The Fiscal Year 2027 defense budget allotted to bunker buster weapons is $429 million, compared to the past decade’s average of $123 million; however, “it will take several years for the bombs to be delivered,” CSIS warns. The shortage comes at a time when the commander in chief is considered escalating military action against Iran.

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