GBU-57 MOP

The GBU-57 Massive Ordnance Penetrator (MOP) was developed under the Big BLU program initiated in 2002 to create heavy conventional munitions. The project was prioritized in 2004 after evaluations from the 2003 invasion of Iraq demonstrated that existing bunker-buster munitions could not consistently destroy deeply buried or hardened targets. Flight testing began in 2007, and the system was delivered for operational use in 2011.

The munition consists of a BLU-127 series bomb body encased in high-density Eglin steel alloy, a material selected to withstand the structural loads of deep earth and concrete penetration. The internal payload includes AFX-757 and PBXN-114 explosives; the latter is a polymer-bonded explosive designed for efficacy in confined spaces. Guidance is provided by a tail-mounted kit containing a GPS-assisted inertial navigation system. The unit is equipped with grid fins rather than standard planar fins, allowing for internal carriage and stability during high-velocity flight. Detonation is managed by the Large Penetrator Smart Fuze, which can be preprogrammed or set to trigger based on the characteristics of the target structure and impact depth. The weapon is intended to strike targets protected by reinforced concrete or rock, although its effectiveness is subject to the compressive strength and density of the specific geological or man-made barriers.

The United States Air Force is the sole operator of the GBU-57. The weapon is integrated for use with the B-2 Spirit strategic bomber and is designated for the B-21 Raider. Initial flight trials were conducted using the B-52 Stratofortress, but that platform is not configured for combat deployment of the munition. The first combat use occurred on June 22, 2025, during strikes against the Fordow Uranium Enrichment Plant and the Natanz Nuclear Facility in Iran. The munition is maintained in an operational stockpile, with production capacity increases scheduled as of 2024.