Factbox-US B-2 bombers and bunker-busters used in Iran strike

WASHINGTON (Reuters) -The U.S. Air Force's B-2 Spirit stealth bombers were involved in strikes on Iran's nuclear sites on Saturday.

Three Iranian nuclear sites were struck in a "very successful attack," President Donald Trump said on Saturday, adding that the crown jewel of Tehran's nuclear program, Fordow, is gone.

The B-2 is one of America's most advanced strategic weapons platforms, capable of entering sophisticated air defenses and delivering precision strikes against hardened targets such as Iran's buried network of nuclear research facilities.

B-2 SPIRIT SPECIFICATIONS:

The U.S. B-2 costs about $2.1 billion each, making it the most expensive military aircraft ever built. Made by Northrop Grumman, the bomber, with its cutting-edge stealth technology, began its production run in the late 1980s but was curbed by the fall of the Soviet Union. Only 21 were made after the Pentagon's planned acquisition program was truncated.

The bomber's range of over 6,000 nautical miles (11,112 km) without refueling enables global strike capabilities from continental U.S. bases. With aerial refueling, the B-2 can reach virtually any target worldwide, as demonstrated in missions from Missouri to Afghanistan and Libya and now Iran. 

Its payload capacity of more than 40,000 pounds (18,144 kg) allows the aircraft to carry a diverse array of conventional and nuclear weapons. The bomber's internal weapons bays are specifically designed to maintain stealth characteristics while accommodating large ordnance loads which could include two GBU-57A/B MOP (Massive Ordnance Penetrator), a 30,000-pound precision-guided "bunker buster" bomb. 

Reports said six bunker buster bombs were used on Iran's Fordow research site. 

The B-2's two-pilot crew configuration reduces personnel requirements while maintaining operational effectiveness through advanced automation systems. 

The B-2's stealth technology incorporates radar-absorbing materials and angular design features that minimize detection by enemy air defense systems. Its radar cross-section is reportedly comparable to that of a small bird, making it nearly invisible to conventional radar.

MASSIVE ORDNANCE PENETRATOR (MOP):

The 30,000-pound MOP represents the largest conventional bomb in the U.S. arsenal, specifically engineered to defeat hardened underground bunkers. Its massive size requires the B-2 to carry only one or two MOPs per mission, but provides unmatched bunker-penetration capability. 

The weapon's 20.5-foot (6.25-m) length and GPS-guided precision targeting system enable accurate strikes against specific underground facilities. Its penetration capability of over 200 feet through hardened concrete makes it effective against the world's most protected underground installations.

CONVENTIONAL PAYLOADS: 

Joint Direct Attack Munitions (JDAM) provide the B-2 with precision conventional strike capability against fixed targets. These GPS-guided weapons can be deployed in large numbers, with the bomber capable of simultaneously engaging multiple targets with high accuracy. 

Joint Standoff Weapons (JSOW) extend the aircraft's engagement range while maintaining stealth characteristics during approach. These glide bombs allow the B-2 to strike targets from outside heavily defended airspace perimeters. 

Joint Air-to-Surface Standoff Missiles (JASSM) offer long-range precision strike capability with their own stealth features. The extended-range JASSM-ER variant provides strike options against targets over 500 miles (805 km) away.

NUCLEAR PAYLOAD CAPABILITIES: 

The B-2 Spirit serves as a key component of America's nuclear triad, capable of delivering strategic nuclear weapons with stealth and precision. The aircraft can carry up to 16 B83 nuclear bombs.

(Reporting by Mike Stone in WashingtonEditing by Marguerita Choy and Sonali Paul)