The B-2 Spirit, America's stealth bomber, remains the only operational aircraft in the US Air Force capable of delivering the Massive Ordnance Penetrator (MOP) bomb.

Designed as a "bunker buster," the MOP is a precision-guided munition weighing 30,000 pounds (14,000 kilograms) and measuring 20.5 feet (6.2 meters) in length.

Its engineering specifically targets deeply buried enemy facilities, cave systems and fortified bunkers resistant to conventional weapons.

On June 22, 2025, seven B-2 Spirit bombers made history during their first combat deployment of the GBU-57 MOP.

Dropping 14 MOPs on Iranian nuclear sites, US forces struck the Fordow Uranium Enrichment Plant and Natanz Nuclear Facility.

The mission showcased the bomb's effectiveness in penetrating reinforced underground targets and highlighted its strategic importance to US strike capabilities.

Precision engineering and tactical design

The GBU-57 MOP outclasses previous "bunker buster" ordinances, including the GBU-28, which the F-15E delivers.

The MOP's larger payload and advanced design make it unmatched in its ability to destroy deeply buried targets.

Its modular BLU-127 bomb body utilizes 5,342 pounds (2,423 kilograms) of explosive material, including AFX-757 and PBXN-114 polymer-bonded explosives.

The steel alloy casing withstands immense stress during impact to ensure penetration prior to detonation.

The integrated GPS/INS guidance system enables precise strikes, with the Large Penetrator Smart Fuze (LPSF) adjusting explosion timing based on depth and structural integrity.

This precision engineering allows the bomb to detonate at the optimal moment for maximum damage.

In flight, grid fins, rather than standard planar fins, stabilize the MOP, providing superior control and trajectory adjustment.

Grid fins are foldable for storage in the B-2 Spirit's bomb bays, ensuring the bomber maintains its low radar signature.

Strategic development and deployment

As part of the US Air Force's "Big BLU" weapons collection, the GBU-57 MOP represents a broader concept for enhanced penetrator and blast weapons.

Developed for deployment by the B-2 Spirit and forthcoming B-21 Raider bombers, the MOP is the most advanced penetrator bomb in the arsenal.

Initial production commenced around 2011–2012, with at least 20 units delivered by 2015, followed by the start of full-scale manufacturing soon after.

The MOP's introduction revolutionizes precision-guided munition capabilities, enhancing US strategic deterrence against fortified underground targets.

Its role in the Fordow and Natanz strikes demonstrated its power against fortified underground facilities critical to hostile infrastructure.

As threats evolve, the MOP remains a pivotal weapon delivering unparalleled reach and precision against protected targets.

The B-2 Spirit, in turn, carries the MOP's legacy forward as a symbol of US superiority in stealth innovation and strike capability.