During the 1993 Waco siege of the Branch Davidians, elements of the Alabama and Texas Army National Guard were called in to assist the ATF and the follow on effort by the Federal Bureau of Investigation; the National Guard's involvement was limited to several specific areas; surveillance and reconnaissance, transport, maintenance and repairs, training and instruction, helicopters, unarmed tactical ground vehicles. The Army National Guard helicopters were also used to do photographic reconnaissance work. Training for ATF agents included such subjects as Close Quarters Combat, and combat medical instruction, and a mock up of the Mount Carmel complex was constructed at Fort Hood, Texas for rehearsals.