I’ve been getting questions from multiple readers about “bunker busting bombs” since the U.S. strike on Iranian nuclear facilities. The bomb in question is the GBU-57 MOP. GBU stands for “guided bomb unit” and MOP stands for “massive ordinance penetrator”. Pictured above, a mockup of a GBU-57 is moved for loading in an Air Force hanger. The bomb itself weighs 33,000 pounds, but it “only” contains 5342 pounds of high explosives. The rest of the weight is its Eglin steel alloy casing and control hardware for guiding the bomb.
The concept of bunker-busting weapons dates back to World War II with the development of Röchling shells by German engineer August Coenders. These were special artillery shells with increased mass density, designed to penetrate fortifications by their sheer momentum.
Various versions of the weapon have been used in combat, but they were smaller and could be carried by standard fighter aircraft. The GBU-57 can only be carried by a B-2 Spirit or a Boeing B-52 Stratofortress. Each can be outfitted to carry two GBU-57s. The photo below shows a mockup GBU-57 loaded into the bomb bay of a B-2. Note people at the bottom for scale:
The GBU-57 is a gravity bomb — when dropped from 50,000 feet (the B-2’s max altitude) it reaches the ground at speeds near Mach 1! The exact speed is, of course, classified, since the speed at impact determines how far it can penetrate into the ground. The US Air Force has stated that the GBU-57 is capable of penetrating up to 200 feet of unspecified material before exploding. Others are claiming penetration up to 200 feet into 5,000 psi reinforced concrete. It is America’s largest non-nuclear bomb. It’s worth noting that Iranian chemists have developed a formula for 30,000 psi concrete, and that was likely used in their fortifications.
Obviously, the depth of penetration depends on two primary factors. First is the height it’s dropped from. The longer it falls the greater the impact speed. Second, the depth depends on what is being penetrated — regular dirt is easy, but the rock of a mountain is more difficult. Fractures or discontinuities in the rock can deflect the bomb from its vertical trajectory, reducing penetration depth.
These bombs cost around $500M each, and we dropped 14 of them onto the Iranian nuclear facilities. That was probably a large part of our inventory, and the first time the GBU-57 had been used in actual combat. As of this writing, the damage assessment is ongoing.
Next Week in Sky Lights ⇒ How Uranium Is Enriched