“It’s none of your business.” With this curt reply to the International Atomic Energy Agency, Iran has shrouded in mystery the engineering wonder and possible strategic horror emerging under Pickaxe Mountain. For defense experts and those following the game of nuclear non-proliferation cat-and-mouse, the drama of this underground complex is less Cold War throwback than masterclass in 21st-century underground war.
The Pickaxe Mountain plant, formally Kūh-e Kolang Gaz Lā, is more than just another entry in Iran’s roster of nuclear facilities. Its engineering is a masterclass in contemporary defense design. Whereas Fordow, once Iran’s “crown jewel” uranium enrichment site, had two tunnel portals and depths ranging from 60 to 90 meters, Pickaxe dwarfs them. Satellite photography and topographic analysis indicate no fewer than four tunnel entrances two on either side of the mountain and subterranean chambers dropping perhaps more than 100 meters below ground, all protected by a mountain 1,608 meters above sea level, more than 50 percent higher than Fordow’s host mountain.
That added height is not only an engineering achievement; it’s a buffer zone. The mass of the mountain and the maze-like tunnel system offer a degree of security that, in the words of Foundation for Defense of Democracies’ Reuel Marc Gerecht, provides Iran “a nuclear weapons site that even the US Air Force would have difficulty destroying with its largest conventional bombs.” Add several tunnels and an impenetrable security perimeter on top of that, and any sabotage or commando incursion becomes even more challenging, a lesson learned from decades of Israeli experience with Hezbollah and Iranian proxies.
The engineering skill on display relies on developments in underground construction techniques. New tunnel boring machinery, sophisticated ground freezing technology, and the incorporation of real-time geotechnical monitoring systems have made it possible to construct huge robust underground areas. As described in a National Academies report, artificial ground freezing and computer-controlled boring permit accurate excavation even under adverse geological conditions, while advanced ventilation and climate control technology enables deep facilities to accommodate sensitive activities.
But even the strongest engineering comes up against the challenge of military technology. The response of the US to Iran’s nuclear ambitions has been the use of the GBU-57/B Massive Ordnance Penetrator (MOP), a 30,000-pound precision-guided bomb that is capable of destroying underground fortresses. When released from high-altitude altitude drops by a B-2 bomber, the ogive-shaped nose and high sectional density of the MOP allow it to penetrate up to 200 feet of concrete or bedrock and then deliver a kinetic impact at speeds above Mach 1. Programmable fuse detonates at specific depths and is designed to take advantage of structural weaknesses like service tunnels or ventilation shafts focusing blast waves to maximize internal damage. But as the recent attacks on Natanz and Fordow showed, even a salvo of these weapons will only “seal off” and not destroy deeply buried facilities, particularly those with redundant tunnels and dense overburden.
The shortcomings of kinetic strikes have led Iran to double down on a dispersal strategy. Before the recent round of bombings, truck convoys were seen outside Fordow, and intelligence estimates report that hundreds if not thousands of sophisticated centrifuges used to enrich uranium to weapons grade were moved to secret locations, potentially including Pickaxe Mountain. Israeli intelligence veteran Sima Shine has pointed out that the secret centrifuge farms hidden away would enable Iran to resume the enrichment process even if known facilities are wiped out.
This hidden relocation is not just a logistics problem; it’s a technological chess move. As noted by the Institute for Science and International Security, Iran’s nuclear equipment now consists of roughly 6,000 sophisticated centrifuges spread across inaccessible sites, many out of reach for IAEA inspectors. The Pickaxe complex with its scope and depth could comfortably accommodate several thousand more, enriching uranium gas to ever-greater purities. As of May 2025, Iran’s stated stockpile comprised 408.6 kg of uranium enriched to 60 percent, a number which has steadily increased as monitoring has decreased.
The consequences of the US and Israeli attacks have revealed a contradiction: by targeting monitored facilities, Western powers might have exchanged known risks for unknown ones. As the Australian Strategic Policy Institute puts it, physical destruction has pushed Iran’s program deeper underground literally and metaphorically making it harder for intelligence to be collected and leaving the way open to covert enrichment. The “blind spot” produced by the destruction of open, inspectable sites might be more perilous than the monitored status quo.
Engineering, here, is not merely concrete and steel; it is defense against, counter to, a war of offense and counter-offense. Iran’s strategy deep tunneling, quick dispersal, and high-tech enrichment demonstrates an advanced appreciation of the limitations of contemporary munitions and the possibilities presented by cutting-edge below-ground construction. The Pickaxe Mountain complex is evidence of this new age of strategic engineering, in which boundaries of civil infrastructure and military defense continue to blur, and in which the bunker versus buster arms race determines the global security scenario.
