81mm Mortar Carrier M4.
From this angle, there is little to differentiate the 81mm mortar carrier M4 from the half-track car M2 on which it was based. (Picture from TM 9-710/TO 19-75A-77.)
A look into the interior, however, reveals the rearward-firing mortar and extra stowage for its ammunition. Seats for the crew flank the mortar, and a rear door has been added. Note the .50cal machine gun, which would be an easy substitution or addition to the specified .30cal machine gun. (Picture from TM 9-710/TO 19-75A-77.)
The rear door is open on this vehicle, but the skate rail would obviously make entry and exit from the rear door somewhat difficult. As noted, more mortar bombs were stowed just behind the usual side ammunition compartments, and these racks can be glimpsed at the side of the passenger compartment. (Picture from Tank Data, vol. 2.)
The machine gun mounts M35 and M35C are shown on the left and right, respectively. These allowed the machine gun to be moved along the rail, as well as be elevated and traversed in the mounts themselves. Traverse in the mounts was restricted to 160° (80° left and right), but the rail ensured 360° coverage. (Picture from TM 9-710/TO 19-75A-77.)
The short body and thick fenders indicate this vehicle was based on the half-track car M2, and the rearward-pointing mortar in the passenger compartment and rear stowage boxes further define it as an M4A1 mortar carrier. On the M4, the mortar would be barely visible from this angle, if at all, since its mount was lower than on the M4A1. The side ammunition compartment door can be seen in front of the mine rack, and the skate rail for the machine gun is visible above the cab. This vehicle is fitted with the demountable headlights and anti-ditching roller. The battery box is positioned on the passenger-side running board.
This machine has the older fender-mounted headlights and is armed with a .30cal machine gun. (Picture from TM 9-710 Basic Half-Track Vehicles (White, Autocar, and Diamond T).)
The rear stowage boxes flank the door added to the passenger compartment. A mortar bomb is visible on the passenger compartment floor, and the holes on the floor are the traversing arc of the mortar. The large 2-pronged bracket above the towing pintle was for stowage of the mortar's baseplate. Normally a hinged platform section would connect the diamond plate platforms under the stowage boxes, but it is missing on this vehicle.
The mount M1 for the 81mm mortar is shown here. On the M4 the mount was fixed, but the M4A1 provided a traversing arc that allowed the bipod's legs to be secured in holes in the rear passenger compartment floor. The large vertical spacer that was added to enable the mortar to traverse is apparent.
Stowage for mortar bombs was provided along the sides of the passenger compartment. The machine gun skate rail is visible to the rear, and a fuel tank is visible in the vehicle's rear corner.
This half-track is fitted with the single-coil spring-loaded idler wheel. The single-coil spring appears visually thinner and less substantial than the double-coil design, and was an interim fix until the double-coil idler wheel could be put into production.
The three crew seats positioned around the mortar are visible in this picture, as well as details of the mortar mount without the ordnance present. Note that the hinged rear platform missing in the above vehicle is also present. (Picture from Standard Nomenclature List G-102.)
The floor stowage compartments on this M4A1 are open. Bows for the canvas cover are stowed on top of the rear stowage boxes, a machine gun tripod is on top of the right-hand box, and bedrolls for the crew are strapped to the rear of the boxes. (Picture from TM 9-710 Basic Half-Track Vehicles (White, Autocar, and Diamond T).)
