Why a 14,000-kg bomb was the only option US had to strike Iran's nuclear Fordow fortress

The US has officially entered Israel’s war on Iran — a move Prime Minister Benjamin Netanyahu had sought from the start.

American warplanes dropped bombs on three nuclear sites in Iran on Saturday, President Donald Trump announced, bringing the U.S. military directly into the war after days of uncertainty about whether he would intervene.

The three sites that Trump said were hit Saturday night included Iran's two major uranium enrichment centers: the mountain facility at Fordow and a larger enrichment plant at Natanz, which Israel struck several days ago with smaller weapons.

Fox News host Sean Hannity, citing a personal conversation with President Trump, revealed that six Massive Ordnance Penetrators, commonly known as “bunker buster” bombs, were dropped on Iran’s Fordow nuclear facility by multiple B-2 bombers.

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For days, Trump weighed whether to supply Israel with the powerful munitions needed to strike Iran’s heavily fortified Fordow facility — a target extremely difficult to hit.

The Fordow site in northwest Iran is the country’s nuclear nerve and required the US’ B-2 bombers— the world’s most expensive military aircraft — to penetrate its defences.

What is a Bunker Buster bomb?
“Bunker buster” is a broad term used to describe bombs that are designed to penetrate deep below the surface before exploding. In this case, it refers to the latest GBU-57 A/B Massive Ordnance Penetrator bomb in the American arsenal. The roughly 30,000 pound (13,600 kilogramme precision-guided bomb is designed to attack deeply buried and hardened bunkers and tunnels, according to the US Air Force.

It's believed to be able to penetrate about 200 feet (61 meters) below the surface before exploding, and the bombs can be dropped one after another, effectively drilling deeper and deeper with each successive blast. It was not immediately known how many were used in the Sunday morning strike.

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The bomb carries a conventional warhead, but the International Atomic Energy Agency has confirmed that Iran is producing highly enriched uranium at Fordow, raising the possibility that nuclear material could be released into the area if the GBU-57 A/B were used to hit the facility. However, Israeli strikes at another Iranian nuclear site, Natanz, on a centrifuge site have caused contamination only at the site itself, not the surrounding area, the IAEA has said. US warplanes also hit Natanz.

Iran’s Fordow fortress
The Fordow plant in the Iran’s northwest is its second nuclear enrichment facility after Natanz, which has already been targeted by Israeli airstrikes.

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Fordow is smaller than Natanz, and is built into the side of a mountain near the city of Qom, about 60 miles (95 kilometers) southwest of Tehran. Construction is believed to have started around 2006 and it became first operational in 2009 — the same year Tehran publicly acknowledged its existence. In addition to being an estimated 80 meters (260 feet) under rock and soil, the site is reportedly protected by Iranian and Russian surface-to-air missile systems.

Only the bunker busters were believed up to the job, and only American aircraft could deliver them.

The plant was impenetrable by any bomb except the GBU-57 Massive Ordnance Penetrator (MOP). The U.S. is the only country in the world that has this “bunker buster” weapon, as well as the only country with the aircraft capable of transporting and deploying it: the B2 Spirit stealth bomber.

ALSO READ: Why the US used B-2 stealth bombers, costing $2.1 billion each to strike Iran’s nuclear sites

This is in part why Israel had been so eager for U.S. involvement in its offensive operations against Iran in addition to its defensive ones.

Moreover, the United States has blocked Israel from getting the bunker buster, and while Israel has fighter jets, it has not developed heavy bombers capable of carrying the weapon.

World's most expensive military aircraft
In theory, the GBU-57 A/B could be dropped by any bomber capable of carrying the weight, but at the moment the US has only configured and programmed its B-2 Spirit stealth bomber to deliver the bomb, according to the Air Force.

The 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.

It is only flown by the Air Force.

According to the manufacturer, the B-2 can carry a payload of 40,000 pounds (18,000 kilograms) but the U.S. Air Force has said it has successfully tested the B-2 loaded with two GBU-57 A/B bunker busters — a total weight of some 60,000 pounds (27,200 kilograms).

The strategic long-range heavy bomber has a range of about 7,000 miles (11,000 kilometers) without refuelling and 11,500 miles (18,500 kilometers) with one refuelling, and can reach any point in the world within hours, according to Northrop Grumman.