US military reveals successor to "bunker buster" bomb already in the works

The US Air Force’s recent combat use of the 13,700 kg GBU-57/B Massive Ordnance Penetrator (MOP) "bunker buster bombs" in strikes on Iranian nuclear sites has renewed attention on the development of its successor. Even when the MOP began entering service in the early 2010s, the US military already had strong interest in a Next Generation Penetrator (NGP).

B-2 Spirit stealth bombers deployed 14 GBU-57/B bombs during last weekend’s Operation Midnight Hammer—12 of them targeting Iran's Fordow enrichment facility and two more striking Natanz. The B-2 remains the only aircraft currently cleared for operational use of the MOP, but according to an article published by The War Zone the upcoming B-21 Raider stealth bomber is expected to be certified to carry them as well. B-52 bombers have used MOPs in testing. While the overall stockpile of MOPs is believed to be relatively small, Bloomberg reported last year that efforts are underway to triple or even quadruple annual production capacity.

The GBU-57/B is a precision-guided bomb, with a warhead designated BLU-127/B. It includes a GPS-assisted inertial navigation system (INS), specialized fuzes, and other components. Despite its massive weight, only about 20 percent of the bomb’s total mass is explosive. The MOP’s diameter is approximately 0.8 meters.

The most recent publicly available requirements for the NGP come from a US Air Force contracting notice issued in February 2024. It calls for a warhead weighing up to 10,000 kilograms, in comparison to the current one weighing up to 2,600 kg, that can produce blast, fragmentation, and penetration effects. However, it does not define a total weight for the munition or specify its dimensions.

“The prototype penetrator warhead design effort should allow integration of technologies acquired and lessons learned under previous penetrator warhead developments to meet performance requirements for the HDBT target set,” the articles cites the Air Force notice stating. “The USAF will consider novel, demonstrated, or fielded Guidance, Navigation & Control (GNC) technologies with viability for integration into a warhead guidance system design that can achieve repeatable, high accuracy performance in GPS aided, degraded, and/or denied environments.”

The Air Force specified a desired “terminal accuracy” of “CE90 w/in 2.2m both in GPS aided, degraded, and denied environments.” In practical terms, that means a munition capable of striking within 2.2 meters of a target point 90 percent of the time—even in conditions where GPS data is limited or unavailable. This is a high standard of precision, especially under degraded conditions. For comparison, Joint Direct Attack Munition (JDAM) bombs can usually strike within five meters when GPS-assisted but may deviate up to 30 meters without GPS. While the exact terminal accuracy of the current MOP is classified, post-strike images from Fordow and Natanz suggest exceptional precision.

The NGP notice also references “possible integration of embedded fuze technology,” though without elaboration. For penetrating munitions like MOP or its successor, reliable fuzing is critical due to the immense stress on the bomb’s components as it bores through hardened structures.

Munitions designed to penetrate deeply into underground facilities require advanced fuzing technology, particularly when pre-strike intelligence does not provide precise data on target depth or structure. For years, the US military has shown particular interest in void-sensing fuzes, which can detect when the bomb has entered an open space like a room in an underground complex. Additionally, the article notes that fuzes capable of “counting” floors to detonate at an optimal depth could significantly enhance destructive effectiveness.

By Nazrin Sadigova