Our Best Look Yet At The Massive Ordnance Penetrator Bunker Buster Bomb

New images released by the U.S. Air Force provide what appears to be our best look yet at a live example of the service’s 30,000-pound class GBU-57/B Massive Ordnance Penetrator bunker buster, or MOP.

The MOP is the most powerful and deeply burrowing non-nuclear bunker buster on earth and is critical to taking out highly fortified targets buried under literal mountains, like those found in Iran, Russia, China, and North Korea. The weapon is guided and can impact the surface above its target with a high degree of accuracy. Typically, the Air Force is very strategic about showing off these unique bombs, making the release of these high-quality images all the more intriguing. 

MOP being moved into position. Whiteman Air Force Base via Facebook

The photos themselves were released on Whiteman Air Force Base’s official Facebook account yesterday. The base is the home to the B-2 Spirit stealth bomber force. As the image caption notes, two MOPs have been added to the arsenal of Whiteman’s 509th Munitions Squadron, in order to test the performance of the weapons, although only one of these appears in the pictures. At present, the B-2 Spirit stealth bomber is the only aircraft able to employ the MOP operationally, although, as The War Zone has noted in the past, B-52 bombers have dropped them during testing. The Air Force’s future B-21 Raider stealth bomber is expected to be able to carry one MOP while the B-2 carries two.

Whiteman Air Force Base via Facebook

Clear details as to which version of the MOP this particular example is, along with its warhead, aren’t provided in the images. However, they do reveal that the bomb was in fact live and filled with high explosives – indicated by the diamond checkered band. rather than a single blue band seen in the past on inert training versions, towards its nose. 

Arguably the most intriguing part of the images relates to the markings describing the unique cocktail of explosives that fill the MOP, which detail their respective weights. They reveal that the weapon pictured was filled with around 4,590 pounds of AFX-757 and about 752 pounds of PBXN-114 for a total of around 5,342 pounds of high-explosive filler. The markings also note the total nominal weight of the MOP as being 27,125 pounds.

Whiteman Air Force Base receives a GBU-57/B Massive Ordnance Penetrator
Whiteman Air Force Base via Facebook

As the Air Force Research Laboratory (AFRL) noted in a past press release about AFX-757’s use in the warhead on the AGM-158 Joint Air-to-Surface Standoff Missile (JASSM), it “was developed and tested through an in-house research project, the Advanced Penetrator Explosive Technology (APET) Program” and “is a propellant-like, plastic bonded explosive (PBX) developed to maximize the blast energy output.”

AFX-757 boasts “higher blast characteristics, is less sensitive to many physical effects which can trigger unwanted explosions, uses less expensive ingredients, and is easier to process than… explosive fills like Tritonal and PBXN-109,” according to AFRL. In addition, “the ingredients of AFX-757 are less expensive. The cost savings over current formulations is significant. It is also easier to process and load into the warhead case.”

PBXN-114 is another kind of insensitive plastic-bonded explosive.

What’s perhaps most compelling about these numbers is that the MOP is only 20% explosive by weight. The vast majority of its heft comes from its super-hardened, dense structure that is capable of borrowing so deep into fortified structures that no other bunker busters can touch. While this ratio isn’t unheard of for much smaller bunker busters, for something that is heavier by a factor of more than five, this is quite fascinating and provides a key detail as to how MOP fulfills its very challenging application.

Close-up view of the MOP’s markings. Whiteman Air Force Base via Facebook
Another view of the MOP’s markings. Whiteman Air Force Base via Facebook

As The War Zone has outlined in the past, MOP development efforts date back to at least 2002. In 2009, Boeing was awarded contracts to complete aircraft integration with MOP. Since then, seven GBU-57 variants have emerged. The GBU-57/B, -57A/B, and -57B/B were fitted with BLU-127/B, -127A/B, and -127B/B warheads, respectively, along with guidance and other components that include fins and tails.

A B-2 dropping a MOP. USAF

Subsequent improvements Boeing made to the GBU-57C/B and -57D/B variants are unclear, although the latter included an upgraded fuze. From 2016 the GBU-57E/B model – likely developed as part of the Enhanced Threat Reduction IV (ETR-IV) upgrade program – has been in the U.S. Air Force’s inventory, fitted with the BLU-127C/B warhead. Little is known specifically about the capabilities of the latest variant, the GBU-57F/B. Regardless, the GBU-57 program is very much an iterative one and these weapons are being continuously enhanced to defeat changing threats abroad.

A B-52 releases a test version of the Massive Ordnance Penetrator (MOP) during a test of the weapon over White Sands Missile Range, New Mexico, in 2009. DoD

Little is known about how many total MOPs have been delivered to the Air Force by Boeing. According to the service, 20 MOPs had been delivered by Boeing (accurate as of November 2015). Beyond this, we just don’t know how many may be in the Air Force’s possession, or how many have been retrofitted with the Enhanced Threat Response-IV (ETR-IV) or other modifications. That number has likely grown substantially due to the growing chances of a major military confrontation abroad.

An MOP mock-up sits inside a training device that simulates a B-2 bomb bay in 2007. U.S. Air Force

Of course, it should be noted that other images of GBU-57/Bs have been posted publicly by the Air Force of late. Back in early April, the 131st Bomb Wing Missouri Air National Guard posted a picture of a GBU-57A/B Massive Ordnance Penetrator (trainer version) to its official Facebook account, pictured at Whiteman AFB’s weapons load trainer facility in March. The MOP seen in that image, unlike the more recent pictures from Whiteman AFB, shows the bomb equipped with its control section and wings attached, including its pop-out grid fins. The blue band indicates its warhead is inert.

Master Sgt. Brock Schuld, 131st Aircraft Maintenance Squadron, gives Missouri National Guard Senior Enlisted Leader Command Sgt. Maj. Larry Godsey a tour of the Whiteman Air Force Base weapons load trainer facility and the dummy munitions that Airmen use to gain proficiency for the B-2 Spirit stealth bomber mission, March 23, 2023. 131st Bomb Wing Missouri Air National Guard via Facebook

Air Force disclosures of MOPs historically have come at moments of heightened tension – designed in part to send a message of U.S. military strength to its adversaries. Indeed, the current flurry of MOP pictures comes amid a spike in geopolitical friction, including between the United States and North Korea over that country’s ballistic missile and nuclear weapons programs. As we have noted in the past, MOPs could prove instrumental in penetrating the various very deeply buried missile tunnels and other underground military facilities in North Korea, China, Iran, and Russia. Such underground networks are well beyond the reach of smaller bunker busters, such as 2,000-pound class BLU-109/Bs or BLU-137/Bs or 5,000-pound class GBU-28/Bs or GBU-72/Bs.

A graphic showing the potential penetration capabilities of the MOP from very early in the program. We don’t know if this is in any way reflective of the present weapon’s capabilities. DOD via GlobalSecurity.org

While the optics of recent MOP images being released are at least in part designed to project U.S. military might to its adversaries, if nothing else they provide an exceptionally detailed look at these extremely heavy bombs.

Contact the author: oliver@thewarzone.com