U.S. Central Command (CENTCOM) drew worldwide attention on March 17 (local time) when it posted on X: "Hours ago, U.S. forces successfully dropped multiple 5,000-pound deep penetrator munitions on Iran's hardened missile bases along the coast near the Strait of Hormuz."
CENTCOM did not disclose exactly which bomb was used. However, U.S. media outlets reported it was the GBU-72. The GBU-72 is a medium-sized bunker buster developed by the U.S. Air Force. Its first aerial drop test was conducted in 2021 via an F-15E Strike Eagle. Full-scale mass production began in 2022.
Deep penetrator munitions, also called bunker busters, are weapons designed to penetrate deep through soil, rock, and reinforced concrete before detonating to precisely strike hardened targets such as underground nuclear facilities or missile bases. In June last year, the U.S. military also dropped GBU-57 super-heavy bunker busters during Operation Midnight Hammer, which destroyed three major underground nuclear facilities inside Iran.
The GBU-57 is an enormous bomb measuring 20.5 feet (approximately 6.2 meters) in length and weighing 30,000 pounds (approximately 13.6 metric tons). By contrast, the GBU-72, at 15 feet (approximately 4.6 meters) long, cannot penetrate as deeply as the GBU-57. However, it serves as a "precision strike drill" weapon system that can be rapidly deployed on fighter jets rather than bombers to hit fortified enemy positions.
GBU (Guided Bomb Unit) series bunker busters are classified as guided munitions. They combine conventional unguided bombs with GPS, INS (inertial navigation system), data links, and laser guidance equipment to enhance strike precision, earning them the label "smart bombs." Encased in steel-alloy shells and equipped with precision guidance systems, these bombs are designed to burrow deep underground before destroying their targets.
What types of laser-guided GBU-series bombs exist? The most prominent bunker busters that penetrate tunnels and underground facilities include the GBU-28, GBU-37, and GBU-57. These add laser guidance kits to general-purpose bombs. A laser designator beams a laser at the target, and the bomb follows the reflected laser beam to guide itself to the target and strike.
