The GBU-57A/B MOP (Massive Ordnance Penetrator), known as a bunker buster, is an American penetrator bomb designed to destroy heavily fortified, deeply buried targets such as underground bunkers, nuclear facilities, or command centers. Development of the bomb began in the early 21st century in response to experiences from the Iraq War (2003), where earlier bombs like the GBU-28 proved insufficient for neutralizing deeply buried targets.
Mock-up of the GBU-57A/B MOP in a B-2A Spirit bomb bay simulator / Photo: USAF
In 2002, Northrop Grumman and Lockheed Martin began work on a 13,600 kg bomb named Big BLU. The project encountered difficulties but was resumed in 2004 under the auspices of the Defense Threat Reduction Agency (DTRA). The first tests were conducted in 2007 in a tunnel at the White Sands Missile Range. Between 2008 and 2010, trial drops were carried out using the B-52H Stratofortress, and integration with the B-2A Spirit was tested starting in 2009. The bomb entered service in 2011.
The program was funded by the DTRA, and in 2009, Congress accelerated its development. In 2011, the unit cost was approximately 3.5 million USD. In 2012, 82 million USD was invested to improve the bomb’s penetration capability. By 2015, at least 20 bombs had been produced; the fourth upgrade was completed in 2018, and additional units were ordered in 2019.
Test Drop from B-52H Stratofortress in 2009 / Photo: USAF
The GBU-57A/B MOP weighs approximately 12,304 kg, measures 6.2 meters in length, and has a diameter of 0.8 meters. It carries a BLU-127 warhead weighing 2,423.5 kg, which includes 2,083 kg of AFX-757 and 340.5 kg of PBXN-114, a mix of HMX and aluminum powder.
The high-strength steel alloy body makes up 80% of the bomb’s total mass. Guidance is provided via a GPS GNSS signal, assisted by an inertial navigation system, resulting in accuracy within a few meters. Grid fins are used for stabilization and trajectory correction during the drop.
The bomb is equipped with a programmable LPSF (Large Penetrator Smart Fuze) with both time and depth delay settings. The GBU-57A/B MOP can penetrate up to 61 meters of 34 MPa concrete, 8 meters of 69 MPa concrete, or between 40 and 100 meters of solid rock.
Test Drop from B-2A Spirit / Photo: USAF
The only certified carrier of the bomb is the Northrop Grumman B-2A Spirit strategic bomber, which can carry two bombs simultaneously, although, as mentioned, it was also tested on the B-52H Stratofortress. In the future, the B-21A Raider is expected to be a platform for the bomb as well.
The combat debut took place on June 22 of this year during Operation Midnight Hammer, when seven B-2As dropped a total of 14 bombs on nuclear targets in Iran — 12 on the Shahid Ali Mohammadi Nuclear Center in Fordow and 2 on the Shahid Ahmad Roshan Nuclear Center in Natanz (earlier reports of use against pro-Iranian Houthis remain unconfirmed).
The GBU-57A/B MOP is the most powerful conventional bunker-penetrating bomb in the U.S. arsenal, crucial for destroying strategic underground targets. It is worth noting that it is often confused with the GBU-43/B MOAB (Massive Ordnance Air Blast), a fuel-air bomb designed for striking surface targets. The MOAB measures 9,190 mm in length, 1,028 mm in diameter, and weighs 9,850 kg, of which 8,482 kg is the H-6 warhead filled with Tritonal — a mix of 80% TNT and 20% powdered aluminum — with a blast yield equivalent to 11 tons of TNT. The GBU-43/B was first used on April 13, 2017, in the Achin district of Nangarhar province in eastern Afghanistan.
