http://online.wsj.com/article/SB10001424127887324582004578459170138890756.html

Pentagon Bulks Up 'Bunker Buster' Bomb to Combat Iran

U.S. Upgrades Weapon to Penetrate Key Nuclear Site; Push to Persuade Israelis

By ADAM ENTOUS and JULIAN E. BARNES
May 2, 2013

WASHINGTON—The Pentagon has redesigned its biggest "bunker buster" bomb with more advanced features intended to enable it to destroy Iran's most heavily fortified and defended nuclear site.

U.S. officials see development of the weapon as critical to convincing Israel that the U.S. has the ability to prevent Iran from getting a nuclear bomb if diplomacy fails, and also that Israel's military can't do that on its own.

Several times in recent weeks, American officials, seeking to demonstrate U.S. capabilities, showed Israeli military and civilian leaders secret Air Force video of an earlier version of the bomb hitting its target in high-altitude testing, and explained what had been done to improve it, according to diplomats who were present.

In the video, the weapon can be seen penetrating the ground within inches of its target, followed by a large underground detonation, according to people who have seen the footage.

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