The idea of the cover was to keep dirt and debris out of the actuator slots and chamber. According to the Auto-Ordnance catalog "with one motion the breech cover can be un- snapped and the gun brought into action. The leather thong then will keep the cover attached to the Thompson until it is needed."

1928Al WITH COVER ATTACHED.

CLOSE UP OF THE LEATHER EDGE ON THE COVER WITH BROAD ARROW MARKINGS.