Master Sergeant Wallace was an officer under the command of Major Welles.
Msgt. Wallace was told by Lt. Murphy to get SPC. Campbell and Cpl. Hank Leavitt, and only finds them in the barracks playing "grabass" with several women. When he was grilling both Leavitt and Campbell, the latter answered back causing Wallace to punch him in the stomach in retaliation. He would have thrashed them both further apart from the fact that Maj. Welles needed them for the operation in Fort Anchorage, Alaska.
Later Sgt. Joseph Capelli finds Wallace and punched him in the face, warning Wallace to never touch his men stating that "in [his] darkest dreams, [he] can't imagine what [they have] been through." Capelli then walks away from Wallace as he gets up and sorts himself.