The Joint Direct Attack Munition is a guidance tail kit that converts existing unguided free-fall bombs into accurate, adverse weather "smart" munitions. With the addition of a new tail section that contains an inertial navigational system and a global positioning system guidance control unit, JDAM improves the accuracy of unguided, general purpose bombs in any weather condition. JDAM is a joint U.S. Air Force and Department of Navy program.
The GBU-31/B is the JDAM version carrying a 2000-pound warhead. The following types of warhead may be used with these tailkits: the standard Mk 84, the BLU-109/B penetrator warhead, the BLU-117A/B, and the BLU-119/B Crash PAD (Prompt Agent defeat) weapon.
The designation GBU-32/B was allocated to the 1000-pound class JDAM bombs. The following types of warhead may be used with these tailkits: the standard Mk 83 and the BLU-110/B for the U.S. Navy, which is externally identical to the MK 83, but uses the PBXN-109 thermally insensitive explosive.