The German architect of one of Saddam Hussein’s main bunkers in Baghdad said on Friday the Iraqi leader can survive anything short of a direct hit with a nuclear bomb if he stays within its four-feet-thick walls.

“It could withstand the shock wave of a nuclear bomb the size of the Hiroshima one detonating 250 meters away,” said Karl Esser, a security consultant who designed the bunker underneath Saddam’s main presidential palace in Baghdad.

U.S.-led troops will also find it hard to fight their way in through its three-ton Swiss-made doors, Esser told Reuters in an interview.

A retired Yugoslav army officer who helped build other bunkers for Saddam also told Reuters this week that the shelters were impenetrable and could survive an atomic bomb.

CNN reported on Friday that U.S. B-52 bombers dropped a two ton “bunker busting” bomb on the capital for the first time in the campaign.

The palace bunker can accommodate 50 people and has two escape tunnels, one leading 200 meters to the Tigris river.