The U.S. Air Force is now reportedly dropping its newest bunker-buster bomb, the 5,000-pound class GBU-72/B, on targets in Iran. The bombs are said to have been used in strikes on hardened Iranian anti-ship cruise missile sites along the highly strategic Strait of Hormuz overnight.

There are also reports that this is the first time GBU-72/Bs have been used in combat, but it is not clear if this is the case.

“Hours ago, U.S. forces successfully employed multiple 5,000-pound deep penetrator munitions on hardened Iranian missile sites along Iran’s coastline near the Strait of Hormuz,” U.S. Central Command (CENTCOM) wrote in a post on X, which did not name the munitions in question, last night. “The Iranian anti-ship cruise missiles in these sites posed a risk to international shipping in the strait.”

“US official confirms this was the GBU-72 Advanced 5K Penetrator,” CNN‘s Haley Britzky subsequently wrote on X. Fox News has also now reported the use of GBU-72/Bs in last night’s strikes.

Whether or not the GBU-72/B has been employed in combat previously is unclear. In 2024, CBS News reported that the Air Force had employed the bombs in strikes on an underground facility belonging to Iranian-backed Houthi militants in Yemen, citing unnamed officials. Fox News also reported again just today that the A5K’s first use had come during previous strikes on the Houthis.

There have also been reports in the past that Israel has at least sought to acquire GBU-72/B, but whether any have been delivered to that country is unknown. It is also still not known what munitions were used in strikes that left three very large and precise holes on the top of a site long linked to Iran’s nuclear program last week. The Israel Defense Forces (IDF) has said they struck that facility, but that does not automatically mean that U.S. forces did not do so, as well.

When reached by TWZ, CENTCOM declined to comment on the specific munitions used in last night’s strikes along the Strait of Hormuz.

The GBU-72/B was developed to replace the older GBU-28/B, which first entered service in 1991. The GBU-28/B is another 5,000-pound class bunker buster, and it is unclear to what degree it remains in U.S. inventory.

What aircraft are currently cleared to employ the GBU-72/B operationally is also not clear. In 2021, the Air Force announced the successful release of an A5K from an F-15E Strike Eagle in testing. In 2024, pictures emerged of a B-1 bomber carrying one of the bombs on an external pylon under the forward fuselage in another apparent test. The Air Force has also raised the possibility of integrating the GBU-72/B onto the B-2 bomber in the past. F-15Es, B-1s, and B-2s are among the aircraft the U.S. military has been using to carry out strikes on targets in Iran.