|Date of first acceptance||March 1943||Total acceptances||3433|
|Manufacturer||International Harvester Corp.||Crew||10 men|
|Height over .50cal MG||108"
|Length with winch||249.06"
|Width over mine racks||86.875"
|.50cal M2HB MG||Flexible on ring mount M49||700 rounds||360°
|.30cal M1919A4 MG||Flexible on pintle mounts||7750 rounds||360°
|Rolled homogeneous steel|
|Location||Thickness||Angle from vertical|
|Engine||International Harvester RED-450-B; 6 cylinder, 4 cycle, in-line gasoline|
|Horsepower||Net: 143@2700rpm||Torque||Net: 348 ft-lb@800rpm||Fuel capacity||60gal
|Transmission||Spicer 1856 constant mesh, 4 speeds forward, 1 reverse|
|Type||Road wheels||Track return rollers|
|Front: Semi-elliptic longitudinal leaf spring
Rear: Vertical volute spring
|Front: Steel ventilated disc
Rear: 1 bogie/track;
|Drive sprockets||Idlers||Shock absorbers||18-tooth front drive||Spring-loaded at rear of track||On front wheels|
|Center guide band type|
|Pitches/track||58||Track ground contact length||46.75"
|Max level road speed||42mph
|Max vertical obstacle||12"
|Min turning diameter||59'
|Max fording depth||32"
|Cruising range||~200mi, roads
The M9A1 resulted from the fact that White and Autocar could not keep pace with the demand for half-track cars, and was analogous to the M2 half-track. M9A1s differed in several respects from the M2A1, however. M9A1s lacked the side ammunition compartments, featured rear doors, the fenders on the M9A1s were flat in cross-section, and unlike the M2A1 the M9A1's body was the same length as the M5's, its personnel carrier counterpart. The M9A1 also never had the large fender-mounted headlights. International Harvester used rolled homogeneous steel armor on their vehicles, which allowed plates to be welded together, giving IHC's half-tracks a smoother appearance than the bolted half-tracks. The rolled homogeneous armor could also be formed, and IHC's half-tracks featured rounded rear corners, which contrast to the right-angled corners on the machines with face-hardened armor. Homogeneous armor lessened the chance of injury due to bullet splash and flying cap screws which could be dislodged when hit, but it was not as strong as face-hardened plate. This meant that the armor on IHC's half-tracks needed to be thicker than the face-hardened armor of the M2A1 to offer the same protection. The M9A1 was therefore fitted with heavier axles and hull strengthening components, but its performance still essentially equalled that of the lighter M2A1. No half-track cars M9 were produced, as the .50cal ring mount modifications had been approved before production began. The M9A1's length with the anti-ditching roller was 242.19" (615.16cm).