The two rear doors for infantry entry and exit are obvious in this rear view. Stowage for fuel or water cans and pioneer tools can also be seen on the vehicle's rear. Towards the front of the vehicle, the semicircular indentation housing a handle is the auxiliary generator and engine access door. Later-production vehicles replaced the spout-type fuel filler with a flat domed cover. (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
The revised fuel filler cover can be seen on this example.
This upper view is of an early-production vehicle. The brush guard does not protect the engine exhaust pipe, and behind the exhaust pipe on the vehicle's right is the auxiliary engine access cover that was not needed on later vehicles that lacked the auxiliary generator. (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
The commander was provided with six stationary vision blocks for use when his cupola door was closed. When the machine gun was mounted, the door could only be opened when the weapon was placed in the travel position, which is illustrated in the view above. (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
The large steering control lever pivoted as one unit, and driver's legs were placed between the arms of the control. The driver also had a horn switch just to the right of the right-hand steering lever arm. The large dial in the center of the instrument panel is the speedometer. (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
The vehicle commander's seat had a total height adjustment of 16.25" (41.28cm) available by pulling the adjustment lever to the left and raising or lowering the seat. The emergency trip lever allowed the seat to be folded down when not in use. The platform was also adjustable by moving it rearward to disengage the two front detents, engaging the desired front detents, and then locking the rear detent with the labeled detent lever. (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
One of the passenger compartment rear doors is shown here, along with part of the bench seat offered for the infantry. The labeled door latch handles were used to turn the cams for the outside door latches that hold the doors open when engaged. Three longitudinal seats were provided for passengers; the left and right were fixed, but the center seat was removable to provide access to the fuel tanks under the passenger compartment floor. (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
The armament rack installed in the rear of the vehicle could hold eight rifles or carbines, two .30cal machine guns, or a mortar. The rear of the rack provided stowage for a rocket launcher, or a steam condenser case and water chest for a .30cal heavy machine gun. The center bench seat is visible in front of the armament rack. The seat cushion on this bench could be swung up to access stowage inside the base of the seat. (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
Two roof doors were provided for the passenger compartment, and these could be locked with 5" or 10" (13cm or 25cm) gaps or in the fully open position. The doors were locked in position by using the detent post. (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
The M75's engine and transmission are pictured here. The engine had overhead valves actuated by a single overhead camshaft for each cylinder bank. A single Stromberg float-type double-venturi downdraft carburetor was mounted. Bore and stroke were both 5.75" (14.6cm), its compression ratio was 6.5:1, and the engine could hold 12 gallons (45L) of oil. Dry weight with the flywheel and all accessories was 1856lb (841.2kg). Including the flywheel assembly, length was 49.24" (125.1cm), width was 50.72" (128.8cm), and height was 36.96" (93.88cm). (Picture from TM 9-755B Full-Track Armored Infantry Vehicle T18E1.)
This is a later-production M75. The access door to the right of the engine, in the sloping plate just behind the engine exhaust pipe, is flat. On earlier vehicles an auxiliary generator was included, and its engine was installed under this access panel, giving it a humped cross section. The driver's hatch is visible on the vehicle's front left corner. The hinges for and outline of the left passenger compartment roof door are just visible to the rear of the vehicle. The large engine access door in the hull front is apparent, and its exhaust pipe is protected by an extension to the right headlight cluster brush guard. The grille on the hull left side is for cooling air exhaust, and the small protuberance in front of this exhaust grille is for external activation of the vehicle's fire suppression system. (Picture courtesy Vincent Scorsone.)
An interesting comparison between the outgoing M75 and its replacement can be made here.