This article previously appeared in Cipher Brief.
The DoW urgently needs to organize its scattered subterranean warfare assets into a single unified organization. Ideally, a Direct Reporting Portfolio Manager (DRPM) for Subterranean Warfare, reporting to the Deputy Secretary of War. (The Department already uses this model for unmanned systems, critical weapons and Golden Dome.) This group would have three portfolios: Subterranean Resilience, Subterranean Sensing and Subterranean Defeat. The office would integrate validated requirements, experimentation, testing, acquisition, and fielding.
Subterranean Resilience
During the 2026 Iran conflict, Iranian ballistic missiles and low-cost drones hit U.S. installations across eight Middle Eastern countries. Hundreds of buildings and structures were damaged or destroyed. The Navy’s Fifth Fleet headquarters in Bahrain was among the installations hit hard. Iranian weapons damaged one E-3 airborne early-warning aircraft and five KC-135 tankers on the ground in Saudi Arabia. (The official inspector-general report documents the damage.) Despite thousands of successful interceptions, the attacks exposed the vulnerability of concentrated, above-ground assets.
The rapid redeployment of the B-1s from RAF Fairford in the UK after warnings of an Iran-linked threat (reported as a possible drone attack) made the point: unsheltered concentrated high-value aircraft are vulnerable even way outside the theater.
The assumptions the U.S. has made about air superiority, missile defense, aircraft dispersal, building hardening, and the survivability of concentrated forward bases were all flawed. While we were prepared for ballistic missiles and hostile aircraft, drone swarms combined with ballistic missiles saturated and got through our defenses.
Washington’s reaction has been to invest billions of dollars in counter-drone and missile defense systems. Yet public budget documents reveal no comparable effort to put vulnerable aircraft, fuel, command-and-control nodes, and munitions out of harm’s way – sheltered, underground (or in space). (Agile Combat Employment, dispersal, hardening, deception, shelters, and rapid runway repair were never designed for a combined drone and missile onslaught.)
The Pentagon has recognized for decades that underground facilities are among the most effective ways an adversary can blunt U.S. conventional superiority. It described that problem explicitly in 1999. Gaza and Ukraine should have made it abundantly clear.
China, Russia, North Korea, and Iran use underground facilities, dispersal, hardening, and deception to make their own high-value assets harder to find, assess, and disable. We need to underground assets that cannot be quickly replaced: command posts, comms nodes, ammunition, fuel distribution points, repair facilities, key power systems, maintenance spares, and high-value aircraft or drones.
The department needs an integrator that coordinates resilience across the Military Departments, Joint Staff, combatant commands, defense agencies, and intelligence community and provides Subterranean Resilience.
However, resilience is only one part of subterranean warfare.
Subterranean Sensing and Defeat
The U.S. needs to know where adversaries’ underground facilities are located, and the internal layout of those facilities. Today, these bespoke exquisite systems for tunnel detection, robotic mapping of accessible tunnels, Hard and Deeply Buried Targets (HDBT) characterization, and target defeat are siloed in organizations scattered across the DoW and other parts of the national security establishment. Most of these systems still require boots on the ground. Once a target is found, Combatant Commands need an integrated system that can characterize and destroy these targets, without first gaining physical access. Today, for the deepest facilities that means bombing from the air. Iran is the case in point.
Background. Iran’s route to a nuclear weapon is by enriching uranium. Natural uranium is composed of 0.71% uranium-235 (U235) and it’s only the U235 that is used to build a bomb.Iran uses centrifuges to separate U235 and increase its concentration (enriching it.) One centrifuge won’t do much, but connecting thousands of centrifuges together into cascades and running them for months can produce pounds of U235 .
2008 President of Iran Mahmoud Ahmadinejad touring Natanz enrichment facility
Iran’s underground nuclear enrichment site at Natanz had well over 10,000 centrifuges installed across dozens of cascades, and their Fordow nuclear enrichment site was built for 16 cascades, roughly 3,000 machines. Before the June 2025 strikes, Iran’s three declared enrichment facilities contained more than 20,000 centrifuges in 125 full-sized cascades.
The rough estimate needed for one Iranian nuclear weapon is ~100 lbs of U-235 at 60% enrichment or 55 lbs of U-235 at 90% enrichment (modern designs use less.) The difference is important, the lighter the weapon the easier it is to fit on a missile.
At its peak (Feb 2025 to June 2025) Iran’s cascades were delivering ~86 lbs of uranium enriched to 60% which is about 50 lbs of U-235 per month, which is just under one potential weapon every month. (Most weapons use U235 enriched to 90+% because that permits a smaller, more reliable design. Getting to that level in Iran might take days or weeks running the cascades, but building it into a weapon would still be needed.)
Deeply Buried Targets Versus Bunker Busters. One of the stated goals of the U.S. strikes on Iran was to remove their capacity to build nuclear weapons. This required the U.S. to destroy their deeply buried underground nuclear enrichment sites. The largest conventional bomb in the U.S. military’s arsenal is the 30,000-pound GBU-57 Massive Ordnance Penetrator, carried by the B-2 Bomber. A 2019 description said it could reach targets as far as 200 feet underground (its actual effectiveness depends on geology, concrete, facility design, entry points, and the use of multiple weapons). The Iranians knew this and built their nuclear enrichment sites underground. The Fordow site is ~260 to 300 feet under limestone and dolomite. The Natanz site is 25 to 160 feet underground, protected by a 25-foot concrete shield. (But public estimates are all over the place.)
Iran declared Isfahan as an enrichment complex to the IAEA the day before the June 2025 strikes; inspectors never got inside it, therefore its depth and geology are unknown, but speculation is that the enrichment complex is 260 to 330 feet underground. Another suspected enrichment facility is in Pickaxe Mountain, where the exact depths, geology, are unknown but estimates put the facility 250 – 330 feet below the summit. Both Isfahan and Pickaxe were Iran’s shift toward “deep mountain basing” to escape the reach of conventional military strikes.
In June 2025 in Operation Midnight Hammer U.S. B-2 bombers dropped 14 GBU-57 bombs on top of Fordow and Natanz. At Isfahan (Esfahan) more than two-dozen submarine-launched Tomahawks hit tunnel entrances and surface targets. In March 2026, strikes at Natanz hit its entrance.
According to the Institute for Science and International Security, the 22,000 centrifuges at Natanz, the Natanz pilot plant, and Fordow are almost certainly wrecked. What may have survived is the enriched uranium, the spare parts, and the people, and that is the problem. The International Atomic Energy Agency estimated (in June 2025) that Iran had about 970 pounds of uranium enriched to 60%; it has since lost track of where it is. Iran’s known uranium conversion capability at Isfahan was damaged, which it needed to turn the stockpile of enriched uranium into a weapon, and there is no public evidence that enrichment has resumed at Natanz, Fordow or Isfahan. We never hit Pickaxe Mountain or the Isfahan enrichment facility with the GBU-57. The strikes have set Iran back, but no one knows for how long.
While the GBU-57 MOP cannot cleanly punch through solid rock, the debate has shifted from an absolute physical destruction calculation to a functional denial calculation—meaning the military’s goal would be to seal Iran’s nuclear assets in a mountain tomb rather than blowing them up directly.
Did We Succeed? Our stated goal was to prevent Iran from rapidly rebuilding the capability to build nuclear weapons, but there’s no certainty that we did that. Repeated airstrikes may have damaged the buried enrichment plants, but we can’t prove it or account for the buried enriched uranium inside. The fact is that it’s extremely difficult to see how much damage the bombs did to Hard and Deeply Buried Targets (HDBTs) from the air, and without inspectors on the ground, knowing for sure is guesswork. Putting boots on the ground would carry enormous costs and risks. Negotiating the removal and inspection of weapons grade uranium would depend on Iranian cooperation and a way to verify we got it all. All bad choices.
There is another emerging option: autonomous drilling equipment.
Subterranean Sensing and Defeat. It’s not hard to imagine that with enough boots on the ground the U.S. could secure a landing zone, fly in drilling equipment and have crews drill hundreds of feet vertically or thousands horizontally to either place sensors and/or explosives. The U.S. has had organizations building specialized equipment and training for breaching tunnels in Combatant Commands and scattered across the DoW for years (DTRA, DARPA, Army ERDC and CAVES and CZ5 programs, SOCOM, Sandia and the Army’s half-billion-dollar underground-training push (2018) and ATP 3-21.51 Subterranean Operations.) One can even imagine that there are teams already trained and equipment ready to go. And one can equally imagine the Iranians are waiting for them.
What’s new is autonomous drills that could provide post-strike bomb damage assessments and/or destroy Hard and Deeply Buried Targets (HDBTs) without seizing the site. They might be inserted covertly; more likely they’d need air cover while they work.
The combination of AI, robotics and autonomy moves this from science fiction to the possible.
Anduril, The Boring Company, Exodigo, Phoenix Boring, Earthgrid and Traysar are possible candidates to deliver these systems. There are likely others as well.
(Disclosure: after my first blog about undergrounding critical assets, I invested and have a financial interest in companies in this space.)
Surface survivability and subterranean sensing and defeat are no longer one Service’s problem, and they won’t be solved by a single system or an incremental fix. Something fundamentally disruptive has changed in the nature of asymmetric warfare and there’s no going back. While we’re actively chasing immediate solutions (Golden Dome, JIATF-401, et al), we need to rethink the nature of force protection, and military and civilian infrastructure protection.
The U.S. needs a coherent protection and survivability strategy across the DoW and all sectors of our economy. This conversation needs to be not only about how we do it, but how we organize it, how we budget and pay for it, and how we rapidly deploy it.
Lessons Learned
- The DoW needs to organize its scattered subterranean assets into a single organization: a Direct Reporting Portfolio Manager (DRPM) for Subterranean Warfare, reporting to the Deputy Secretary of War
- It should have three portfolios – Resilience, Sensing and Defeat
- Providing validated requirements, experimentation, testing, acquisition, and fielding to Combatant Commands.
- Protection and survivability solutions are not as sexy as buying aircraft or weapons systems but they may be the key to winning a war.
- Subterranean Sensing and Defeat need to move from bespoke special-operations capabilities into standard doctrine.
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