Armored Personnel Carrier M113
The box-like hull was assembled by welding 5083 aluminum alloy rolled plate 11/2 inches thick on the roof, front, and rear. The sides and floor were 1 3/4 and 1 1/8 inches thick respectively. The ramp at the rear was hydraulically operated and also contained a door for use when the ramp was closed. All openings had watertight seals to permit amphibious operation.
The power pack was in the right front hull consisting of the Chrysler Model 75M (M75), liquid-cooled, gasoline engine with the Allison TX200-2 transmission. This V8 engine developed 215 gross horsepower at 4,000 rpm. It was connected to the transmission through a transfer case with a 1:1 gear ratio. The transmission had six forward speeds and one reverse and it shifted automatically between the speeds in each shift range.
These ranges were 1-2, 3-4, 3-5, 3-6, reverse, and neutral. To provide steering, the power was transmitted through a controlled differential at the front of the power plant compartment and then to the final drives and sprockets at the front of each track. The vehicle was supported on a flat track torsion bar suspension with five dual road wheels per side.
Track tension was maintained by an hydraulically adjusted idler at the rear of each track. The single pin, center guide, steel tracks were 15 inches wide and were fitted with detachable rubber pads. The air drop weight of the M113 was 18,600 pounds and its combat weight was estimated to be 22,900 pounds. With a fuel capacity of 80 gallons, the cruising range was about 200 miles. It could reach a maximum speed of 40 miles per hour on a level road.
In water, the freeboard was about 14 inches when combat loaded. Propelled by track action in the water, the M113 could reach a forward speed of approximately 31/2miles per hour. Needless to say, amphibious operations were restricted to calm water as the vehicle was not intended for use in surf or rough water.
For cold weather operation, a winterization kit was provided. This consisted of a personnel heater installed in the right front of the troop compartment. Ducts distributed heat to the troop compartment and to the battery box at the right rear. Hot air could be diverted from the troop compartment to the power plant compartment to aid starting in cold weather.
To use the carrier as an ambulance, a kit was available to install four litters in the troop compartment. These litters were supported by chains attached to the roof and floor. A total of 14,813 M113s were built by the time production ended in 1968. United States forces received 4,974 vehicles and 9,839 were allocated to foreign military sales.
In June 1959, even before production began on the M113, a contract was awarded to evaluate the use of a commercial, compression ignition, engine in the new armored personnel carrier M113. This was in line with the policy to develop a line of diesel powered combat vehicles. This study concluded that the M113 could easily be modified to use the General Motors 6V53, liquid-cooled, diesel engine. Various data sheets rated this V6, two stroke cycle, power plant at 210-215 gross horsepower at 2,800 rpm. A 212 horsepower figure was used for the data sheets in this volume.
The engine was coupled to the Allison XTG-90-2 transmission which incorporated a torque converter with four manually selected speeds forward and one reverse. It included geared steering in the 2nd, 3 rd, and 4th forward speed ranges and clutch brake steering in 1st and reverse. This eliminated the need for the controlled differential required in the M113. It was expected that the elimination of the controlled differential would compensate for the heavier weight of the diesel engine.
FMC Corporation built three engineering pilot vehicles using the new power train and they were designated as the armored personnel carrier M113E1. Tests at Aberdeen Proving Ground, Fort Knox, and Fort Greely revealed numerous transmission failures resulting in its modification and a new designation as the XTG-90-2A. The tests also revealed that the performance with the new power train was superior in all respects to that of the M113. Fuel economy of the new diesel engine increased the cruising range of the M113E1 to about 250 miles compared to the 200 miles of the M113 using the same 80 gallon fuel (light) tank. The use of diesel fuel also reduced the fire danger.
During this same period, FMC Corporation proposed the construction of additional pilots powered by the 6V53 engine with an Allison TX-100 automatic transmission. Since steering was not incorporated in the TX-100, the use of the DS-200 controlled differential was required as in the M113. It was expected that this power train would reduce manufacturing costs. The proposal was approved and FMC built three pilot vehicles designated as the armored personnel carrier M113E2.
The fuel tank capacity in the M113E2 also was increased to 95 gallons providing a cruising range of about 300 miles. Tests of the M113E2 were highly successful and it was classified as the full-tracked armored personnel carrier M113A1, Standard A, by U.S. Army Materiel Command Technical Committee Minutes (AMCTCM) Item 950 on 16 May 1963. After completion of two preproduction pilots, full production of the M113A1 began at FMC in late 1964.
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