In 2002, Northrop Grumman and Lockheed Martin were working on the development of a earth-penetrating weapon, said to be known as "Big BLU". But funding and technical difficulties resulted in the development work being abandoned. Following the 2003 invasion of Iraq, analysis of sites that had been attacked with bunker buster bombs revealed poor penetration and inadequate levels of destruction. This renewed interest in the development of a larger bunker buster, and the MOP project was initiated by the Defense Threat Reduction Agency to fulfill a long-standing Air Force requirement.