"The Air Force built a weapon so big it was nicknamed "Mother of All Bombs" on the eve of the war with Iraq, but MOAB would be dwarfed by a much larger munition now under study. The proposed Massive Ordnance Penetrator, or MOP, would weigh 30,000 pounds, nearly 40 percent more than the 21,000 pound MOAB -- officially Massive Ordnance Air Blast -- that never saw combat. "The reason it's heavier than MOAB is that it has to penetrate a target," said Fred Davis, technical director for assessment and demonstrations at the Air Force Research Laboratory's Munitions Directorate. MOP would be designed to explode deep in the ground or inside a structure to destroy tunnels and bunkers or topple tall buildings."