A new defense analysis estimates that America’s stockpile of its most powerful conventional bunker-busting bombs has fallen to the low single digits, raising concerns about military readiness as President Donald Trump considers further operations against Iran.
By yourNEWS Media Newsroom
The United States may face significant limitations in its ability to strike heavily fortified Iranian military facilities as supplies of specialized bunker-busting weapons decline and Tehran expands its network of underground installations, according to a new assessment by the Center for Strategic and International Studies.
The October 15 CSIS analysis, prepared by retired Marine Corps Col. Mark Cancian and research associate Chris Park, estimates that the U.S. military has only a handful of its largest conventional penetrating bombs remaining following earlier operations against Iran’s nuclear infrastructure.
The findings arrive as President Donald Trump considers additional military action against Iranian targets that have survived previous American and Israeli strikes. The researchers warn that replenishing specialized weapons inventories could take years, creating a gap between immediate military requirements and future production.
Among the weapons facing the greatest inventory pressure is the GBU-57 Massive Ordnance Penetrator, a 30,000-pound bomb designed to attack deeply buried and heavily reinforced facilities.
According to CSIS, American forces used 14 Massive Ordnance Penetrators during Operation Midnight Hammer, which targeted Iranian nuclear facilities at Fordow and Natanz.
Although publicly available records indicate that the Air Force received at least 20 of the bombs, the precise inventory remains classified. The researchers estimate that the number remaining is in the low single digits.
The Trump administration subsequently redirected $123 million toward replenishing the inventory. However, manufacturing and delivering replacement weapons will require several years, limiting how quickly depleted stocks can be restored.
The findings do not indicate that the United States has exhausted its entire supply of bunker-busting weapons. The researchers distinguished between the comparatively large inventory of smaller penetrating bombs and the limited availability of heavier munitions needed against exceptionally hardened targets.
Those differences have become increasingly important as adversaries construct military facilities deeper underground.
Bunker busters are specialized weapons designed to penetrate protective layers of soil, rock or concrete before detonating. Unlike conventional bombs, they typically use reinforced steel casings and comparatively smaller explosive charges to maximize their ability to reach protected structures.
Many can be fitted with laser-guidance or GPS-based systems that enable aircraft to strike designated targets with greater precision.
The U.S. arsenal includes several categories of penetrating weapons, ranging from 2,000-pound bombs to much heavier munitions developed specifically for underground installations.
One example is the 5,000-pound BLU-113, which was developed to penetrate heavily fortified structures. Newer weapons, including the BLU-138 Advanced 5,000-Pound Penetrator, are intended to improve performance against protected targets.
The Massive Ordnance Penetrator represents a more specialized capability, carrying approximately 5,700 pounds of explosives within its reinforced body.
The weapon was designed for exceptionally difficult targets, including underground nuclear installations and military command facilities.
However, CSIS warned that some Iranian installations may now be situated beyond the effective reach of existing conventional weapons.
The researchers identified Iran’s Pickaxe Mountain nuclear complex as a particular concern because the site is believed to be buried deeper than previously targeted installations.
Construction at Pickaxe Mountain reportedly remains underway, leaving uncertainty about the facility’s operational status and the precise activities conducted there.
Nevertheless, its depth presents a potential challenge for American military planners seeking to eliminate Iran’s underground nuclear capabilities.
The analysis also highlighted reports of 33 underground Iranian missile bases near the Strait of Hormuz that may have survived previous strikes.
Continuing Iranian missile launches suggest that at least some protected missile and drone storage facilities remain operational, according to the researchers.
Those installations illustrate a broader military challenge: fortified underground networks can preserve weapons, equipment and personnel even when surface infrastructure is heavily damaged.
The CSIS assessment, also highlighted in a social media report on the Pentagon’s penetrating-weapons inventory, comes amid renewed debate about America’s ability to sustain prolonged military operations involving heavily defended targets.
The concern extends beyond Iran.
China and North Korea have invested extensively in underground military infrastructure, including tunnel networks, command centers and facilities associated with missile and nuclear operations.
Armed groups have also relied on fortified underground structures to protect personnel and equipment against conventional airstrikes.
The development reflects a military competition in which advances in precision-guided weapons encourage adversaries to place valuable assets farther below the surface.
For American defense planners, the challenge involves maintaining sufficient quantities of penetrating weapons while developing systems capable of reaching increasingly hardened facilities.
The Pentagon’s proposed fiscal 2027 defense budget reflects that growing demand.
According to CSIS, the administration requested $429 million for conventional bunker-busting weapons, compared with an inflation-adjusted annual average of approximately $123 million during the preceding decade.
The proposed funding represents a substantial increase in planned procurement spending, although additional appropriations cannot immediately translate into available weapons.
Specialized bombs require manufacturing capacity, components, testing and delivery schedules that can extend over multiple years.
The researchers also identified operational limitations involving the aircraft needed to deliver heavy bunker-busting bombs.
Because the weapons rely on substantial weight and reinforced construction, most must be released from aircraft operating relatively close to their targets.
That requirement can expose aircraft to enemy air defenses, particularly in conflicts where the United States has not established control of the surrounding airspace.
Developing longer-range penetrating weapons could reduce those risks, but the available arsenal remains heavily dependent on air-dropped bombs.
The analysis noted that nuclear weapons remain a separate theoretical option against targets beyond the capabilities of conventional munitions. Their inclusion reflects the range of weapons historically considered for hardened facilities, not an indication that nuclear use has been authorized or recommended for Iran.
CSIS emphasized that the central procurement challenge involves two different requirements: maintaining adequate quantities of weapons for relatively common underground targets and preserving specialized capabilities against the deepest installations.
Smaller penetrating bombs may be sufficient for tunnels, bunkers and less heavily fortified facilities, while major underground complexes require weapons with greater penetrating power.
The shortage is particularly relevant to the administration’s consideration of further strikes against Iran.
Trump has repeatedly stated that Iran must not obtain nuclear weapons and has discussed the possibility of additional military operations against facilities that remain beyond the reach of previous attacks.
The Defense Department did not immediately respond to a request for comment from the Daily Caller News Foundation regarding the reported inventory concerns.
Because exact weapons stocks are not publicly disclosed, the CSIS estimates cannot be independently confirmed from available procurement figures alone.
Nevertheless, the analysis identifies a significant gap between the increasing number of hardened military targets and the production capacity required to maintain specialized munitions.
The researchers concluded that the demand for bunker-busting weapons is likely to continue growing as adversaries expand underground infrastructure to protect high-value assets from precision strikes.
For the United States, the immediate issue is whether existing supplies can support potential military operations before additional weapons enter service.
With replacement bombs requiring years to manufacture and Iran continuing to develop underground facilities, the findings raise questions about how effectively American forces could sustain repeated attacks against the country’s most heavily protected targets.
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