This is the GBU-57 MOP bomb. MOP stands for Massive Ordnance Penetrator, it is a non-nuclear munition and it belongs to the Americans.

It is the only bomb thought to be capable of hitting key Iranian nuclear targets buried deep beneath the mountains.

Fourteen MOPs were dropped by the US across two nuclear sites at the weekend.

The Fordow Fuel Enrichment Plant near the city of Qom is about 95 miles southwest of Tehran and it is believed to store crucial centrifuges for enriching uranium.

The site is built into the side of the mountain, an estimated 80 metres beneath soil and rock.

During Operation Rising Lion, the Israeli Air Force damaged the Iranian nuclear programme, but it was not destroyed because the Israelis have no ordnance that can reach them. 

There is believed to be only one non-nuclear bomb in service capable of reaching these underground facilities – the 30,000lb GBU-57 – and there is only one aircraft capable of carrying it – the B-2 Spirit stealth bomber. 

Known for its "bunker-busting" capability, the GBU-57 can strike targets as deep as 61 metres and with multiple hits, it is believed to be able to penetrate even deeper.

Up until now, it has only been used in tests, but the Americans used its predecessor, the 15,000lb BLU-82 Daisy Cutter bombs, during the Vietnam War, dropping them from the back of Hercules to clear helicopter landing areas in the jungle. 

They were also used in the first Gulf War and against al-Qaeda in the Tora Bora caves of Afghanistan after 9/11 in 2001. 

The next giant US bomb was the GBU-43 Massive Ordnance Air Blast, known as a MOAB, and nicknamed the Mother of All Bombs. 

MOAB contained 18,700lbs of explosive and was used against an ISIS cave complex in Afghanistan in 2017. 

If the US decides to support Israel in its action action Iran, it is likely to be the B-2 stealth bombers leading the way. 

It was the B-2 stealth bomber that led the way, dropping the MOPs, followed by a salvo of submarine-launched missiles that hit Iran's nuclear facilities as US president Donald Trump ordered an attack on Iran's nuclear programme.

Each B-2 can carry two GBU-57s. There were six stealth bombers based at Diego Garcia in the Indian Ocean until early May this year, but they returned to Whiteman Air Force Base in Missouri and are believed to have been replaced by B-52s at Diego Garcia. 

The first MOP was dropped on the site at Fordow at 02:10 on Sunday, with a total of 14 MOPs dropped across two of Iran's nuclear sites.

The site at Fordow is reportedly protected by Iranian and Russian surface-to-air missile system, although it is believed the Israeli Air Force has largely suppressed the Iranian air defence systems and has rendered the Iranian Air Force ineffective. 

America already has the USS Vinson Carrier Strike Group in the Arabian Sea and the USS Nimitz CSG on the way from the east.