America's Largest Bomb is Not Nuclear: GBU-57
This is the bomb the Israelis wished they had to attack the Iranian nuclear sites. It is America's biggest bomb in history - the GBU 57, bunker buster that can be dropped with precision down a hole and dig deep inside a mountain before exploding. This is the bomb that would be the only bomb that MIGHT work in destroying some of Iran's underground nuclear facilities.
The bomb is 30,000 lbs., 20 feet long and packs 5,300 of explosives. It can penetrate earth, like a mole, much deeper than before prior to exploding with earthquake-like shaking. However, it would take a few of them to penetrate and destroy any underground fortified facility like Iran has. The first bomb would create the crater or entrance for the others to follow. Each B2 bomber can only carry two such bombs. The newer versions of the bomb cost $82 million each, development costs came to $300 million. The U.S. has not more than 20 of them, of which, 12 are the new improved versions.
The bombs destructive power occurs because of the 80% TNT and 20% aluminum mixture, the latter intensifies the TNT explosion. They were originally built for Iraq's bunkers.The bomb can penetrate 200 feet of hardened concrete.
The Israelis have a smaller version, the GBU-28, it weighs 5000 lbs. These are bunker busting bombs also. They have 55 of them.
Experts tend to doubt whether such bombs will ever be used because it will require multiple flights and the element of surprise would be lost. Also, Iran has known about the capabilities since 2007 and probably have taken into account when building the underground sites. However, they could render the sites unusable for years and delay what seems to be the inevitable.