Scout Car M4 (T13).
The canvas top obscures the skate mount for the .50cal machine gun, which ran around the inner circumference of the vehicle's armor. A folding armored flap was provided for the windshield, and the side armor flap can be seen folded down on the outside of the passenger door. (Picture from Development of Armored Vehicles, volume II: Armored Cars, Scout Cars, and Personnel Carriers.)
The canvas cover is removed, revealing the machine gun skate rail. The gun on its mount can be seen at the front of the passenger compartment. (Picture from Weapon Mounts for Secondary Armament.)
A staff sergeant is shown using the machine gun. The mount here is a modified C-12 adapter and type H1 ammunition holder. The C-12 adapter had a goose-neck shaped pintle. (Picture from Weapon Mounts for Secondary Armament.)
A different machine gun skate mount is seen here fitted with a .30cal machine gun. This mount, derived from aircraft skate mounts, was composed of the carriage assembly, the adapter T12 with pintle, and the machine gun cradle and ammunition box. The pintle was secured in the carriage via a quick-disconnect socket which had positions for being locked or free-turning. (Picture from Weapon Mounts for Secondary Armament.)
