The U.S. military dropped a 2,000-pound (about 907 kilograms) "bunker buster" toward Isfahan, the strategic heart of Iran. Analysts said the strike likely went beyond simple retaliation and may have directly targeted highly enriched uranium that Iran hid deep underground.
On the 30th (local time), the Wall Street Journal (WSJ), citing a U.S. government official, reported that the U.S. military struck a large ammunition depot in Isfahan the previous night with a 2,000-pound (about 907 kilograms) bunker buster. President Donald Trump released a 30-second video of the explosion on his social media (SNS) platform Truth Social. A bunker buster is an earth-penetrating weapon designed to pierce ground and structures with its own weight and detonate at the target point.
◇ Foreshadowing of the "blue barrels" spotted a year ago
The attack came two days after the French daily Le Monde released satellite images of the Isfahan nuclear facility. On the 28th, Le Monde analyzed satellite photos taken on June 9, 2025, and revealed a large transport convoy heading to the Isfahan nuclear facility. According to Le Monde, a truck carrying 18 blue drums entered an underground tunnel, followed by a truck equipped with a crane and three small cars that appeared to be civilian vehicles. Coincidentally, four days after these photos were taken, on June 13, 2025, Israel struck across Iran and the war began.
Le Monde said such a large movement being spotted at the entrance to the Isfahan nuclear facility was unusual. David Albright, a former adviser to the International Atomic Energy Agency (IAEA) and founder of the Institute for Science and International Security (ISIS), said, "This photo shows that Iran recognized Isfahan could come under attack and moved something into the tunnel just before the war in June 2025."
Experts are leaning toward the possibility that the cargo was highly enriched uranium. They said the sealed drum form, the limited load, and what appeared to be a single movement match the characteristics of moving a core "strategic asset." At the time, the IAEA said Iran possessed hundreds of kilograms of uranium enriched up to 60%, and estimated that a significant amount was stored at the Isfahan facility.
However, during the airstrikes in June last year, the U.S. military focused on destroying surface facilities, and there were no indications that the interior of the underground tunnels was destroyed. This raises the possibility that key material was preserved deep underground. On Mar. 9, the IAEA also announced that nearly half of Iran's stockpile of 60% enriched uranium was stored in the Isfahan tunnel complex and likely remains there.
◇ Bunker busters zero in on the underground core
The bunker busters used this time are different in nature. Given that the weapon penetrates tens of meters underground before detonating, analysts said the strike likely aimed not only to destroy facilities but to target the very space where the nuclear material moved at the time was hidden. India's NDTV emphasized the precision of the attack, saying, "Bunker busters reach targets deep enough that ordinary bombs cannot, and they control the timing of detonation."
Ultimately, the strike is being interpreted as a precision hit aimed at the existence of nuclear material moved just before the war, or as a signaling attack to pressure Iran amid uncertainty over its location. There have been no signs of radiation leakage detected on the ground in Isfahan, but observers said the possibility of additional precision strikes by the U.S. military cannot be ruled out.