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WASHINGTON — Efforts to improve the performance of the U.S. military’s heaviest “bunker-buster” bomb have succeeded, according to the Pentagon’s testing chief.

Tests of the 30,000-pound Massive Ordnance Penetrator made by Boeing demonstrated the redesigned weapon “is capable of effectively prosecuting selected hardened, deeply buried targets,” Michael Gilmore, the Pentagon’s director of operational testing, said in a report to Congress.

Pentagon officials have said the 30,000-pound (13,600- kilogram) bomb could be used if the United States decides to attack Iran’s nuclear program, with its deeply buried and hardened Fordo uranium enrichment facility that holds a stockpile of enriched uranium.

While Gilmore didn’t mention any specific uses for the bomb, he said it is intended to hit targets “requiring significant penetration” that are located in “well-protected facilities.”

The testing assessment is the first public discussion of the bomb’s capabilities since early last year, when the Pentagon disclosed a need to improve it.

Testing of modifications involved five bomb drops from B-2 stealth bombers at White Sands Missile Range in New Mexico from June to October and two ground tests, according to Gilmore’s annual report on Pentagon testing, which he sent to Congress on Jan. 11.

The bomb is six times bigger than the 5,000-pound bunker-buster that the U.S. Air Force and the Israeli Air Force have in their arsenals to attack deeply buried nuclear, biological or chemical sites.

Israel has said it may launch an attack on its own, raising questions about whether it could effectively halt Iran’s nuclear program unless the U.S. joined in with the bigger bomb.

Iran, which is under pressure from economic sanctions imposed by the U.S. and the European Union, has said its nuclear program is for civilian purposes.

U.S. Air Force Lt. Gen. Herbert Carlisle cited the 30,000-pound bomb at an industry conference in March as among U.S. capabilities in a potential attack on Iran.

The bomb made by Boeing has “great capability and we are continuing to make it better,” he said. “It is part of our arsenal if it is needed in that kind of scenario.”

The move to improve the bomb was made shortly after the Air Force took the first delivery in September 2011. The action may have been a response to Iran’s announcement on Jan. 9, 2012, that it would begin uranium enrichment at the Fordo facility near Qom that’s tunneled into mountains, said Kenneth Katzman, a Middle East military analyst for the nonpartisan Congressional Research Service in Washington.

“This is a very hard target, and the international community believes that if Iran were to attempt a nuclear breakout, it would be conducted at this site,” Katzman said last year.

The Pentagon won congressional approval in February 2012 to shift $81.6 million in funds to improve the bunker-buster.

The Pentagon request to upgrade the bomb was submitted 11 days after the International Atomic Energy Agency confirmed the enrichment activity. The location at Qom is 90 meters (295 feet) under rock, according to David Albright, founder and president of the Institute for Science and International Security in Washington.

Northrop Grumman’s B-2 stealth bomber is the only aircraft capable of carrying the weapon.

Pentagon Comptroller Robert Hale said in a Jan. 20, 2012, request to Congress that the money was needed to “fix issues identified in testing, including tail-fin modifications and integrating a second fuse, enhance weapon capabilities, build test targets and conduct live weapon testing. The request funds the immediate requirement to support the desired upgrade schedule.”

The 20.5-footlong 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.

The bomb has a hardened-steel casing and can reach targets as far as 200 feet underground before exploding, according to a December 2007 statement by the Air Force News Service.