The Air Force is moving forward with a fourth round of upgrades to Boeing's Massive Ordnance Penetrator -- a 30,000-pound bunker-busting bomb designed to hit targets such as deeply buried clandestine nuclear-weapons development sites -- after a variant of the GBU-57 with a third round of classified upgrades passed muster with the Pentagon's top weapons tester. The Air Force, which is buying and upgrading the largest conventional explosive in the U.S. military arsenal to attack deeply buried and hardened bunkers...
