50 caliber machine gun, armored infantry vehicle
NEW ARMORED PERSONNEL CARRIERS (continuation)
As constructed, the pilot vehicles differed in several details from the mock-up. The T18 was still armed with the two remote control 50 caliber machine gun, but the assistant driver position was eliminated on this and all the other pilots.
The original Т18E1 pilot was unarmed with a high cupola installed in the hull roof for the vehicle commander. The T18E2 was fitted with the T122 machine gun mount in place of the commander's cupola. This mount could be armed with either .30 caliber or 50 caliber machine gun.
On both the T18E1 and the T18E2, a special seat was installed for the vehicle commander below the cupola or machine gun mount. The remaining personnel (carriers) were seated in three longitudinal rows in the rear compartment. At this stage, a total crew of 13 was specified.
Although the original T18E1 pilot was unarmed, the commander's cupola was replaced on later vehicles by a variety of machine gun mounts. When the T18E1 was selected for production, a low silhouette commander's cupola with six vision blocks was installed. It was fitted with a 50 caliber machine gun on an external mount. The small T10 (No. 8396700) domed cupola with an internally mounted .30 caliber machine gun was installed experimentally.
Later, the M13 cupola armed with a 50 caliber machine gun was evaluated on the T18E1. The pilots had a small oil filter access cover in the front upper hull door, but it was eliminated on the production vehicles. Some pilots also had a small ventilation grill at the top rear of the hull side armor. The pilots were fitted with two large folding doors in the roof of the personnel compartment. On production vehicles, they were replaced by two smaller, non-folding, doors, one on each side of the roof.
The original pilots were powered by the six cylinder, air-cooled, AO-895-2 Continental engine. The mufflers for this engine were located in the cooling air exhaust ducts behind the power plant. The engine exhaust was then discharged with the cooling air through the hull side grilles. The later AO-895-4 engine was installed in the production vehicles with a single muffler on top of the engine.
A separate tail pipe carried the engine exhaust through the hull roof and to the right side of the vehicle. Later, the brush guard for the right headlight group was extended to protect the tail pipe. The AO-895 engine developed 375 gross horsepower and was coupled to a CD-500 cross drive transmission.
The torsion bar suspension supported the vehicle on five dual road wheels per side with a compensating idler at the rear of each track. Three track support rollers were on each side. The 21 inch wide, single pin, tracks were driven by the front mounted sprockets. Later, a flat track suspension without support rollers was evaluated on the T18.(U.S. Army)
Production order T-24478, dated 11 January 1950, authorized procurement of five T18 type vehicles for the Field Service Division. This was reduced to two on 3 January 1952 and the remaining three were completed as T73 armored infantry vehicle.
An auxiliary generator and a armored personnel (carriers) heater were installed in the right front hull alongside the engine compartment on the early production T18Els. Later, they were removed and they were not included on the later production vehicles. On 18 January 1951, OCM 33541 changed the nomenclature from armored utility vehicles T18, T18E1, and T18E2 to full-tracked armored infantry vehicle T18, T18E1, and T18E2.
Standardized later as the full-tracked armored infantry vehicle M75 (see also M24), the T18E1 entered production at the International Harvester Company (IHC) and at the Food Machinery and Chemical (FMC) Corporation. The initial contracts were for 1,000 vehicles at IHC and 730 at FMC. Later, FMC produced an additional 50 vehicles bringing the total production run to 1,780.
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