August 8, 2011: After nearly a decade of development, the U.S. Air Force has ordered eight MOP (massive ordnance penetrator) GBU-57A/B bunker buster bombs. These 14 ton weapons cost $3.5 million each. In the last few years, several B-2 bombers have been equipped to carry these weapons (two bombs per B-2). This was apparently meant to send a message to Iran and North Korea. There were no known targets for such a weapon in Iraq or Afghanistan, but there are plenty of such targets in Iran and North Korea. Moreover, even were there deep bunkers in Iraq or Afghanistan, you didn't need a stealth bomber to deliver a MOP. The enemy in those countries have no way of detecting a high flying B-52, much less a stealthy B-2.
The 6.2 meter (20.5 foot) long MOP has a thick steel cap, and can penetrate up to 7.9-61 meters (26-200 feet) of concrete (depending on degree of hardness) or up to 61 meters of rocky earth, before exploding.