Air raids in World War II proved just how devastating aircraft could be. In response, militaries worldwide began digging deep—literally—constructing bunkers and command posts buried dozens of meters underground, shielded by thick layers of reinforced concrete. Ordinary bombs couldn’t touch them, and even U.S. airpower often fell short.
A dramatic example came during the Battle of Iwo Jima, vividly portrayed in the 2006 film Letters from Iwo Jima, despite relentless bombing and naval shelling, Japanese troops—hidden in a web of underground bunkers—held out against U.S. forces for weeks, inflicting over 28,000 American casualties.
Lessons From Iwo Jima to Iraq
The U.S. military learned a hard truth: destroying underground military targets requires more than raw firepower. It requires precision—and penetration.
But instead of developing large bunker-busting bombs, Cold War strategy prioritized tactical nuclear weapons. That changed during the Gulf War in 1991, when Saddam Hussein’s regime buried key facilities deep underground. In response, the U.S. rushed to create the GBU-28, a 2.1-ton “bunker buster” built from surplus Army howitzer barrels and armed with high-powered explosives and laser guidance. Before detonation, it could pierce 100 feet of soil—or six meters of reinforced concrete.
South Korea later acquired the GBU-28, deploying 150 units by 2014 to arm F-15K fighter jets in case of a strike on North Korean nuclear sites or artillery bunkers.
When Weather Got in the Way: Enter the GBU-37
The GBU-28 worked—but not in all conditions. Its laser guidance system was less effective in bad weather. The U.S. developed the GBU-37 in 1997, outfitted with GPS and inertial navigation to address this. However, with a shorter range, it could strike with precision regardless of visibility.
These bombs saw use in Afghanistan in 2001 and again in Iraq in 2003. Yet, even then, some deeply buried bunkers survived. The message was clear: the U.S. needed something even bigger.
The GBU-57: A 14-Ton Monster
That led to the creation of the GBU-57 Massive Ordnance Penetrator (MOP) in 2010—the most powerful conventional bomb in the U.S. arsenal. Weighing 14 tons and over 17 feet long, it can punch through up to 100 meters of earth—or 60 meters of concrete—before exploding.
Only one aircraft can carry the GBU-57: the radar-evading B-2 stealth bomber. Unlike the B-52 or B-1B, which require air defense suppression before entering hostile airspace, the B-2 can slip in undetected and deliver the MOP directly above a target. That stealth capability makes it the go-to option for deep-strike missions.
Recently, three B-2s were deployed to Andersen Air Force Base in Guam, sparking speculation that the U.S. may be positioning GBU-57s to deter—or prepare for—potential threats from North Korea.
The “Mother of All Bombs” and Beyond
While the GBU-57 is unmatched in penetrating power, it’s not the only heavyweight in the U.S. arsenal. In April 2017, during operations against ISIS in Afghanistan, the U.S. dropped the GBU-43/B Massive Ordnance Air Blast (MOAB)—nicknamed the “Mother of All Bombs.” Weighing 22,000 pounds and stretching 20 feet in length, it delivered a blast radius of nearly a mile.
Unlike bunker busters designed to burrow, the MOAB explodes above ground, creating a massive shockwave and heat pressure capable of collapsing tunnels and underground hideouts. Its 18,700-pound warhead creates an oxygen-deprived vacuum within a 1,800-foot radius, instantly annihilating anything in its path.
Russia later responded with its own version—the ATBIP, dubbed the “Father of All Bombs”—claiming four times the explosive power of the MOAB, although these claims remain unverified.
Strategic Tools in a New Era
From Iwo Jima to Baghdad and beyond, the U.S. has continuously adapted its arsenal to address evolving battlefield challenges. Today’s bunker busters and massive ordnance bombs aren’t just relics of brute force—they’re strategic tools in an era of hidden threats and fortified targets.
Whether it’s a nuclear command post or a terrorist tunnel network, the U.S. military now has weapons designed to reach where no conventional bomb could go before.
