GBU-57A/B MOP

The GBU-57A/B MOP (Massive Ordnance Penetrator) is a precision-guided, 30,000-pound (14,000 kg) "bunker buster" bomb used by the United States Air Force. The GBU-57 (Guided Bomb Unit-57) is substantially larger than the deepest-penetrating bunker busters previously available, the 5,000-pound (2,300 kg) GBU-28 and GBU-37. Due to its size (6 meters length and a weight of over 12 tonnes) it can only be carried by large bombers—for instance, the B-2 Spirit.
It is designed to accomplish a difficult, complicated mission of reaching and destroying an adversary's weapons of mass destruction located in well-protected facilities.
In 2002, Northrop Grumman and Lockheed Martin were working on the development of a 30,000-pound (13,600 kg) earth-penetrating weapon, 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.
The U.S. Air Force has not officially communicated a specific military requirement for an ultra-large bomb, but has a concept for a collection of very large penetrator and blast weapons: the so-called "Big BLU" collection, which includes the MOAB (Massive Ordnance Air Blast) bomb. Development of the MOP was performed at the Air Force Research Laboratory, Munitions Directorate, Eglin Air Force Base, Florida with design and testing work performed by Boeing. It is intended that the bomb will be deployed on the B-2 Spirit, and will be guided using GPS. It is also planned to be deployed on the B-21 Raider.
In July 2007, Northrop Grumman announced a $2.5-million stealth-bomber refit contract. Each of the U.S. Air Force's B-2s is to be able to carry two 14-ton MOPs.
In March 2007, an initial explosive test of the MOP took place in a tunnel belonging to the Defense Threat Reduction Agency (DTRA) at the White Sands Missile Range in New Mexico.
In October 2009, ABC News reported that the Pentagon had requested and obtained permission from the U.S. Congress to shift funding in order to accelerate the project. It was later announced that funding delays and enhancements to the planned test schedule meant the bomb would not be deployable until December 2010, six months later than the original availability date.
The project has had at least one successful Flight Test MOP launch.
In April 2011, the USAF ordered eight MOPs plus supporting equipment, for $28 million.
In September 2011, the Air Force took delivery of 20 bombs, designed to be delivered by the B-2 bomber. In February 2012, Congress approved $81.6 million to further develop and improve the weapon.
In November 2011, Bloomberg reported that the Air Force Global Strike Command started receiving the Massive Ordnance Penetrator and that the deliveries "will meet requirements for the current operational need". The Air Force had received delivery of 16 MOPs as of November 2011. In March 2012, there was an "operational stockpile" at Whiteman Air Force Base.
In 2012, the Pentagon requested $82 million to develop greater penetration power for the existing weapon. A 2013 report stated that the development had been a success, and B-2 integration testing began that year.
In June 2010, USAF Lt. Gen. Philip M. Breedlove said that the Next Generation Penetrator (NGP) munition should be about a third the size of the Massive Ordnance Penetrator, so it could be carried by affordable aircraft. In December 2010, the USAF had a Broad Agency Announcement (BAA) for the Next Generation Penetrator.
In 2011, Global Strike Command indicated that one of the objectives for the Next-Generation Bomber is for it to carry a weapon with the effects of the Massive Ordnance Penetrator. This would either be with the same weapon, or a smaller weapon that uses rocket power, not unlike the World War II British/American Disney bomb used, to reach sufficient speed to match the penetrating power of the larger weapon.
One of the current limitations of the MOP is that it lacks a void-sensing fuze and will therefore detonate only after it has come to a stop, even if it has passed the target area.