In March President Barack Obama reportedly offered Israel bunker-buster bombs and other advanced weapons in exchange for a postponing an attack on Iran's nuclear facilities until 2013.
At the time the White House denied that any such agreement was proposed or reached.
Bunker-busters are essential for an attack on Iran's underground nuclear facilities since they can penetrate Tehran's world renowned reinforced concrete.
This week the U.S. Department of Defense notified Congress of a $647 million agreement to provide the Israel Air Force with 10,000 bombs – more than half of which are bunker-busters – along with 6,900 joint direct attack munitions (JDAM) tail kits, which convert unguided free-fall bombs into satellite-guided “smart” weapons.
Haaretz reported that the deal would serve to “renew the inventory of the Israel Defense Forces following the massive bombings in Gaza during Operation Pillar of Defense,” and no doubt it will, but this is a pretty spectacular array of ordnance well beyond what Israel against Gaza last month.
Israel flew about 1,500 aerial bomb attacks in Operation Pillar of Defense, and reports on Twitter of bunker-busters came only sporadically in the latter half of the eight-day campaign. (Israel dropped Israeli-made bunker-busters on Gaza in '08 as well.)
And the last time the U.S. sent Israel bunker-busters, in 2009, the sale included 55 GBU-28 Hard Target Penetrators. This time around the U.S. is providing 1,725 BLU-109 and 3,450 GBU-39 bunker-buster bombs.
Last year The New York Times reported the U.S. refrained from sending the massive munitions before 2009 because “there were deep concerns that if the United States supplied bunker-busting bombs to Israel, it might be viewed as having tacitly endorsed an attack on Iran.”
In any case Israel would most likely need U.S. help to attack Iran because Tehran's Fordow facility is 295 feet underground.
The only weapon that can reach it is America's biggest bomb, the Massive Ordnance Penetrator (MOP). MOPs, each packing 5,300 pounds of explosives, are capable of penetrating 60 feet of reinforced concrete and detonating at more than 200 feet below ground.