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.
The rear stowage boxes flank the door added to the passenger compartment. The skate rail would make entry and exit from the rear door more difficult, as can be imagined. 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. 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 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. Note that the hinged rear platform missing in the above vehicle is also present. (Picture from TM 9-710 Basic Half-Track Vehicles (White, Autocar, and Diamond T).)