Analysis/ How did the US use penetrating bombs on Iran's nuclear facilities?

The penetrating bombs that the United States dropped on two nuclear facilities in Iran were custom-made and were the result of more than 15 years of work in the field of weapons discovery and development, senior Pentagon leaders said Thursday.

Defense Secretary Pete Hegseth and General Dan Caine, chairman of the Army Joint Chiefs of Staff, said in a press conference that they were confident the weapons struck exactly as planned.

Caine, the country's top military officer, provided new details about the work that went into building "bunker-busting" bombs and how the US used them to penetrate Iranian facilities.

He tried to show the extent of the destruction, but did not directly comment on President Donald Trump's statement that Tehran's nuclear program has been "completely destroyed."

The bombs – called the GBU-57 A/B Massive Ordnance Penetrator – were created after a secret briefing, several decades ago, that spoke of a large construction project in the mountains of Iran, Caine said.

The project turned out to be the fuel enrichment plant at Fordo, which is believed to have begun construction around 2006.

It became operational in 2009 – the year Tehran publicly acknowledged its existence.

The classified information was shared with a Defense Threat Reduction Agency official in 2009. He and a colleague “focused completely” on the Fordow facility for the next 15 years, studying the soil, the construction work, the earthworks and “every piece of equipment that went in and out of that place,” Caine said.

What they found was that the US didn't have a bomb that could destroy those facilities. So the Pentagon had to start work on developing one, Caine said.

"We had a lot of experts with PhDs working on a testing program, doing modeling and simulations. In fact, we were the largest users of supercomputers in the US, although we did this in secret," he said.

The bomb, weighing about 13,600 kilograms, consists of steel, explosives and a fuse, which is programmed to explode at a certain time.

The longer the fuse, the deeper the bomb will penetrate the ground before exploding.

Over the years, the military tested and retested the bomb hundreds of times in simulated facilities, Caine said.

Ford had two main ventilation routes leading into the underground facility, and officials carefully monitored these entry points to use as targets to strike the plant.

Each of them had three vertical tunnels – one main tunnel and two smaller tunnels on each side, which on the Pentagon's graphics looked like a three-pronged fork.

Before the U.S. attack, Iran placed large concrete slabs over them to protect them, Caine said.

To respond, the US devised an attack plan that would use six deep-penetrating bombs, one for each of the two ventilation routes.

They would mainly hit the main tunnel, which led to the plant where fuel enrichment was carried out.

Seven B-2 bombers flew, each carrying two large bombs. The first bomb was used to destroy the concrete slab, Caine said.

Four other bombs fell in the main tunnel and penetrated deep into the plant at a very high speed – more than 300 meters per second – before exploding, he explained.

The sixth bomb was kept in reserve, in case something went wrong.

In addition to the 12 bombs dropped on Fordow – six on each of two ventilation shafts – two more hit Iran's main facility at Natanz, Caine said.

Each crew confirmed that the bombs had exploded because they saw them being dropped from the planes flying in front of them.

"We know that the planes that were following behind saw the weapons in action," Caine said.

The pilots reported it was the brightest explosion they had ever seen – it looked like it was daylight, he said.

The location of Iran's highly enriched uranium is not very clear.

Caine said the munitions were properly built, tested and loaded, were accurately aimed at their targets and exploded as planned.

"Iran's nuclear facilities have been destroyed," Hegseth said.

However, it is not yet known whether highly enriched uranium, which Iran could use to make nuclear weapons, was there at the time of the attack.

Asked several times, Hegseth did not answer whether the uranium had been destroyed or moved.

"I haven't seen any intelligence that would tell me that things weren't in their place — whether they were moved or otherwise," Hegseth said./ Associated Press