The second bomb that was fitted with a GAM guidance kit was the 2000 kg (4500 lb) class BLU-113/B "bunker buster" penetrator warhead, which had been developed on a "crash" basis for Operation Desert Storm in 1991 (for details, see GBU-28/B Paveway III). The GAM-equipped BLU-113/B, also known as "GAM-113", was designated GBU-37/B. The first drop of a GBU-37/B from a B-2 occurred in May 1997, and it's possible that weapons of this type were operationally used in Afghanistan in 2001 (but reports are conflicting). The GBU-37/B is replaced by the GBU-28C/B, a development of the GBU-28/B laser-guided bomb with an improved warhead and additional GPS/INS guidance.