The United States has it, and Israel does not.

The Massive Ordnance Penetrator (MOP), which is 6m long, weighs 13,600kg, and has never been fired in anger, was developed to destroy bunkers that other weapons could not reach.

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Technically identified as the GBU-57F/B, it is approved as an operational payload to be launched only by the strategic B-2 Spirit stealth bomber, although tests have also been carried out with B-52s.

President Trump has not joined Israel in taking military action against Iran, but there has been a build-up of warships, carriers and fighter aircraft in the Middle East, ready to carry out strikes.

The clearest sign that Trump had decided to join Israel in trying to eliminate the threat of Iran developing nuclear bombs would be the arrival of B-2s at the British-owned Indian Ocean island of Diego Garcia. Six B-2s were sent there in April as a show of force to Tehran, although in the end they were involved in missions against Houthi targets in Yemen. No MOPs were deployed or used.

Even this huge bunker-busting bomb would face a challenge to reach Iran’s deepest clandestine nuclear facilities, at least some of which are known to be about half a mile — or about 800m — down, beneath layers of reinforced concrete.

The latest version of the MOP has been fitted with a smart fuse that delays detonation until the maximum penetration has been achieved, reported to be more than 60m of concrete. The explosion would have a chance of destroying what was beneath it.

By comparison, Israel has GBU-28 bunker busters, which can penetrate only 6m of concrete. It has not been supplied with the MOP; the US Air Force is believed to have limited supplies, perhaps no more than 20.

In preparation for a potential US strike against Iran, Trump has already approved the dispatch of a second aircraft carrier to the Middle East. The USS Carl Vinson battle group is operating alongside the USS Nimitz carrier with accompanying warships in the Red Sea and Eastern Mediterranean after the Nimitz was redeployed from the South China Sea to the Middle East.

In its Operation Rising Lion, Israeli F-35s have succeeded in carving a relatively invulnerable aerial pathway towards Iran’s four nuclear facilities by targeting the country’s air defence systems with multiple raids. That same pathway could be used by the B-2 or other US aircraft to hit the plants suspected of developing Iranian nuclear warheads.

The Times