At the time of the attack, FSB Mary Ann was garrisoned by Charlie Company, 1/46th Infantry (75 men commanded by Capt Richard V. Knight). In addition, 18 men from Echo Company's Reconnaissance Platoon were at the base preparing for an operation the following day. These troops shared space with 34 support personnel (medics, radiomen, etc.) from 1/46th Infantry's Headquarters Company (HHC). The rest of the garrison (less the ARVN artillerymen) came from elements of Alpha, Bravo, and Delta companies, 1/46th Infantry (22 men who were in transit between their units and areas further to the rear), and assorted artillery personnel (including the crew of a quad-.50 caliber machine gun from Battery G, 55th Air Defense Artillery Regiment). According to one source all ground surveillance radars and night vision (starlite) scopes formerly at Mary Ann were "sent to the Battalion rear for maintenance." This left the base with a series of ground sensors designed to detect movement located "within fifteen hundred to forty-eight hundred meters" of the perimeter. These sensors had been picking up movement since shortly after the base was reopened, but no contact had ever resulted from the readings.