• Bloomberg


The U.S. Air Force has deployed an upgraded version of the country’s largest non-nuclear bomb — a 30,000-pound “bunker-buster” that can only be carried by the B-2 stealth bomber and could be used against adversaries such as North Korea.

A fourth upgrade to the Boeing Co. bomb, the GBU-57, has been completed and the existing inventory is being retrofitted, Capt. Emily Grabowski, an Air Force spokeswoman, said in an email. The modification “has improved the performance against hard and deeply buried targets,” she said.

Bombs known as bunker-busters have been in the air force’s arsenal for years for potential attacks against buried targets. The GBU-57, which is six times bigger than the 5,000-pound bomb the air force has had for years, could be used if the U.S. decided to hit underground nuclear or missile facilities in North Korea, as tensions persist over Kim Jong Un’s growing nuclear arsenal.

Three B-2 bombers were deployed to Guam this month in what the air force said was a planned rotation. Grabowski declined to say whether the GBU-57 has also been sent to the Pacific region.

In May, the air force dropped three of the bombs from B-2s over the White Sands Missile Range in New Mexico, in a test that demonstrated the weapon’s effectiveness, said Army Lt. Col. Michelle Baldanza, a spokeswoman for the Pentagon’s combat testing office.

The test office prepared an “early fielding” assessment in November that deemed the weapon effective “when paired with proper tactics, techniques, and procedures,” the office said in its annual report to Congress.

The GBU-57, also known as the Massive Ordnance Penetrator, is bigger than the 21,600-pound bomb that drew the world’s attention in April, when the U.S. dropped it on an Islamic State target in Afghanistan.

That bomb can only be dropped by pushing it out of an MC-130 propeller aircraft and “is primarily intended for soft to medium surface targets covering extended areas, targets contained in an environment such as caves or canyons, clearing extensive mine fields, and for psychological effects,” air force spokeswoman Ann Stefanek said in an email.

Little authoritative information has been published about the capability of the GBU-57. A December 2007 story by the Air Force News Service said it has a hardened-steel casing and can reach targets as deep as 200 feet (61 meters) underground before exploding.

The 20.5-foot-long bomb carries more than 5,300 pounds of explosives and is guided by Global Positioning System satellites, according to a description on the website of the Pentagon’s Defense Threat Reduction Agency.

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