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In U.S. military weapons development, the BLU-121 warhead, which can use several guidance techniques, is intended to attack specific types of hard targets, such as defended caves or certain bunkers. Because it is optimized for skip bombing across a horizontal surface, rather than deep penetration, its characteristics have similarities to, but differences from, hard target penetrator bombs intended for vertical attack from high altitude. It was reported to have been developed, starting in 2001, as a successor to the BLU-118, by the United States Pacific Command for potential use against hardened North Korean targets, although it is under the broader Hard Target Defeat program of the Defense Threat Reduction Agency. [1]

It has a new hardened case, made from a tougher and cheaper steel, ES-1c, than the Aermet 100 used in the BLU-113 penetrator. It is also filled with a new explosive, AFX-757, which is insensitive to the shocks of hitting the ground, going through blast doors, or anything except the programmed triggering of its fuze. [2] AFX-757 is also part of a new formulation of thermobaric explosives, which combines insensitive high explosives with "a finely particulate metal oxide and a reducing metal to each primary explosive", much like the redox reaction of thermite.[3] Concern has been expressed that the existing hard target FMU-143 fuzes may not be sufficiently reliable against exceptionally hard targets, and the Hard Target Void Sensing Fuze will be implemented in the near future. [4]

The primary delivery aircraft for the BLU-121 will be the F-15E Strike Eagle, which has desirable low-altitude attack capabilities. F-16 Fighting Falcon and B-2 Spirit aircraft are also being certified to use the BLU-121. "Ellwood National Forge Co., Irvine, Pa., was awarded a contract which will exercise an option to procure 108 BLU-121 bombs to be used on precision guided air-to-surface weapons and Joint Direct Attack Munitions for the F-15E, F-16, and B-2 platforms."[5]

Guidance and detonation software follows the rules of a new class of "precise time of arrival munitions", for which as many as six separate bombs can be delivered to explode simultaneously on the same target. Work on precise time of arrival was begun in 2003, and the Defense Threat Reduction Agency described successful tests in 2006. [2]


  1. BLU-121/B thermobaric warhead (United States), Bombs - Precision and guided munitions, Jane'sTemplate:Dead link
  2. 2.0 2.1 David Hambling (January/February 2008), "Groundbreaking Bomb", Defense Technology International, p. 14
  3. John W. Jones (20 January 2004), Energy Dense Explosive, U.S. Patent & Trademark Office, U.S. Patent 6679960
  4. Elizabeth "Betsy" T. Thorn (23 May 2007), 2007 USAF Fuze Acquisition Roadmap, National Defense Industrial Association
  5. Contracts: Air Force, U.S. Department of Defense, 8 April 2010