GBU-57 MOP

The GBU-57 Massive Ordnance Penetrator (MOP) originated from the United States Air Force "Big BLU" program initiated in 2002. Although initially paused due to funding and technical difficulties, the project resumed after bomb damage assessments from the 2003 invasion of Iraq revealed that existing bunker busters failed to destroy certain fortified targets. In 2004, the military formalized a requirement for a heavy, precision-guided munition capable of striking deep underground facilities. Testing began in 2007 using rocket sleds and aircraft, leading to the integration of the weapon onto the B-2 Spirit bomber. The Air Force began receiving the munition in 2011, and plans to expand production capacity were announced in 2024.

The GBU-57 utilizes a BLU-127 series bomb body, which features a modular design to accommodate upgrades. The weapon's casing is constructed from high-density Eglin steel alloy to withstand the physical impact of deep penetration. Its explosive payload consists of AFX-757 and PBXN-114 polymer-bonded explosives, which are formulated for controlled detonation within confined spaces. Guidance is provided by a tail-kit containing a GPS-assisted inertial navigation system. Unlike conventional bombs with planar fins, the GBU-57 employs grid fins that fold to fit inside bomber weapons bays and provide flight control at high speeds. Detonation is controlled by the Large Penetrator Smart Fuze, which can be preprogrammed to detonate at specific depths or dynamically adjust its timing based on the characteristics of the target structure.

The United States Air Force is the sole operator of the GBU-57. The B-2 Spirit strategic bomber is the primary operational platform for the weapon, and integration is planned for the B-21 Raider. While the B-52 Stratofortress was used during the testing phase, it requires modifications for combat employment. The GBU-57 was first used in combat on June 22, 2025, during strikes against Iranian nuclear sites, where B-2 Spirit bombers dropped the munitions on the Fordow Uranium Enrichment Plant and the Natanz Nuclear Facility. The weapon was deployed again during the 2026 Iran war. The munition's capability to defeat deeply buried targets depends on geological factors, as high-strength concrete and hard rock formations can affect penetration depth.