Less than two years after ordering its first eight MOP (massive ordnance penetrator) GBU-57A/B bunker buster bombs, the U.S. Air Force announced unspecified improvements to the deep penetrating weapon. Seven of the first eight production model bombs were used for tests, which resulted in a classified list of possible tweaks to the existing design.
These 14 ton weapons contain 2.4 tons of explosives and 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 anywhere else, but there are plenty of such targets in Iran and North Korea. Moreover, even if there were deep bunkers in Somalia or Afghanistan you don't need a stealth bomber to deliver an MOP. The enemy in those countries have no way of detecting a high flying B-52, much less a stealthy B-2.
But Iran and North Korea do have radars, and a B-2 could slip past those radars and take out the air defense system command bunkers, or any other targets buried deep. The 6.2 meter (20.5 foot) long MOP has a thick steel cap, which was originally designed to 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. This was the original spec, which is now supposed to be improved. A new Iranian nuclear facility (Fordo) is under 90 meters of earth and rock.