The giant “mother of all bombs” dropped on an Islamic State target in eastern Afghanistan on Thursday marked the largest non-nuclear bomb ever used in combat. It’s the second-heaviest non-nuclear bomb in the American arsenal.
A bigger version can be packed into the B-2 stealth bomber based at Whiteman Air Force Base near Knob Noster, Mo.
That 30,000-pound satellite-guided bomb — the Pentagon calls it the GBU-57 Massive Ordnance Penetrator — might be considered the father of all bombs.
The 22,000-pound bomb used in Afghanistan is the GBU-43/B Massive Ordnance Air Blast, or MOAB. It’s typically fused to detonate above its target and uses shock waves to destroy things on and below the ground.
In contrast, the MOP was built to burrow into the ground and then explode. A B-2, which can carry up to 160 smaller bombs, can carry just two on a flight. Special cranes are needed to load the behemoths.
In a recent interview with The Star at Whiteman, B-2 pilot Lt. Col. Justin “Vapor” Grieve compared releasing 500-pound weapons like those used in a January attack over Libya to letting go of the 30,000-pound bombs in testing and training exercises.
“The 500-pound weapon is pretty anti-climactic. What is exciting is when we release our 30,000-pound MOP, the Massive Ordnance Penetrator,” he said. “When you release that, you can feel it. The plane will actually raise up about 100 feet, and then it’ll settle back down. It’s pretty cool. It’s fun.”
Some published reports suggest the MOP, which has never been used in combat, could dig 200 feet into the earth before its 5,300 pounds of explosives detonate. Analysts differ on whether that’s realistic.
The bomb’s metal needed to be strong enough to withstand being dropped on a bunker, a target that might be made of steel-reinforced concrete, and its shape had to be slender enough to pierce the ground like a needle into your skin.
The relatively skinny shape — they stretch 20.5 feet long with a 31.5-inch diameter — is why the heavier bomb made for the B-2 can carry less than a third as much H6 explosive as the MOAB.
A 2005 paper published by the Union of Concerned Scientists discussed the potential damage of bunker-busting and its limits.
“By exploding just a few meters underground instead of at or above the surface, a much larger fraction of the energy of the explosion is transmitted to the ground,” the document said. “The explosion creates a strong seismic shock wave that propagates and can crush or damage an underground bunker. …
“Nevertheless, even nuclear weapons have limited effectiveness at destroying the deepest or widely separated underground bunkers,” the report continued. “For example, an earth penetrating weapon using the 1.2 megaton B83 warhead — the highest yield weapon in the U.S. nuclear stockpile — could crush underground bunkers to a depth of about 1000 feet. Deeper bunkers can be constructed with modern tunneling equipment, and are essentially invulnerable to nuclear attack.”
Boeing made 20 of the B-2’s bunker busters, delivered and tested in 2011, for $30 million. The Air Force has not said how many remain in the arsenal after testing at White Sands Missile Range in New Mexico.
Analysts have long seen the MOP as a potential weapon to be used on deeply buried nuclear weapons programs in Iran and North Korea.
That’s one reason why they’ve been fitted to the B-2 bomber. The stealth jet is used rarely, typically on targets where air defenses pose a significant threat and a plane virtually invisible to radar can sneak through on a first-strike bombing run.
In the recent Afghanistan bombing, the MOAB was dropped from an MC-130 cargo plane. Islamic State fighters on the ground had no way to shoot down a plane. That meant there would be little need to risk one of Whiteman’s 20 B-2s, jets that cost $2 billion-and-counting and are essentially irreplaceable.
In Iran or North Korea, a jet without radar-dodging powers might easily get shot down. That makes the B-2 a more likely candidate — along with standoff weapons like the Tomahawk cruise missiles used earlier in April on a Syrian airfield.
The MOAB was largely designed for what the military strategists consider “softer” targets — infantry troops and nonarmored vehicles. It also could prove devastating for the sort of compound hit in Afghanistan, a relatively primitive tunnel complex that lacked the steel- or concrete-hardened bunkers found at critical locations in Iran or North Korea.
“So if you’re trying to block cave entrances or collapse rudimentary tunnel complexes, you might use the MOAB,” said Mark Gunzinger, a former B-52 pilot and senior fellow at the Center for Strategic and Budgetary Assessments. “If you’re trying to penetrate a very hardened, very deep structure, you might want something to penetrate into the target or to a deep enough depth that you cause damage inside.
“You have to select the kind of weapon you want to use,” he said. “It’s not always a bigger blast.”