One of the most famous armored vehicles of all time and perhaps the most widely used and varied is the Armored Personnel Carrier M113. A vehicle originally designed in the 1950’s to a tight budget has become, due to its simplicity and low cost, a legend in its own right.
The roots of the M113 go back to June 1954, when Detroit Arsenal began to consider a whole family of lightweight vehicles with a common chassis for the US military. The Army Field Forces were sufficiently impressed with the idea that, in September that year, produced the outline characteristics they wanted to see in this family. Two basic configurations were considered; ‘light’ (8,000 lbs – 3.63 tonnes) and ‘heavy’ (16,000 lbs – 7.26 tonnes), and both were to be considered in wheeled and tracked configurations.
Early configuration for the 10-man tracked carrier concept circa 1954/55. Photo: Presdio Press.
The development of these ideas went to Continental Army Command (CONARC) in June 1955 and the 10-man tracked carrier had been expanded to take twelve instead (2 crew and 10 troops). In January 1956, CONARC, having considered these proposals, approved the development of this family of vehicles to cover this tracked carrier (now to carry 13 men) designated T113, a smaller version for 4 men designated T114 and some wheeled variants.
Food Machinery and Chemical Corporation (FMC)
The mockup for the T113 by FMC was finished and inspected in October 1956 and approval was given for the production of tests vehicles. The T113 built from aluminum was also tested in steel and, to avoid confusion, received a different number – T117 – to differentiate the two hulls. Tested for ergonomics and ballistic efficiency, they both had some serious issues, but nothing which could not be addressed. The most significant concern was the level of protection required. Both were weak and, although the steel version was better, it was the aluminum one (T113) which received approval, as it was lighter, although it was recommended that it should be improved to at least match the ballistic protection offered by the T117.
Pilot models of the T113. Photo: Presidio Press
In late 1957, the requirements for the armored personnel carrier for the Army was changed by CONARC. The new vehicle would have to meet tight budgetary constraints, particularly in the engine department, and would have to have improved armor over earlier vehicles.
Two proposals were considered: the first, the T113E1 (name assigned October 1958) was a lightweight vehicle – just 17,500 lbs (7.94 tonnes) – designed with an emphasis on use by airborne troops; the second, the T113E2 (name assigned October 1958) was to be heavier and better protected than the lighter version as well as the predecessor vehicle, the M59. It was to weigh 24,000lbs (10.9 tonnes). Four prototypes of each proposal were ordered by the military.
T113E2 during testing. The hull is unpainted marked just as ‘T113E2 Pilot’. Photo: Presidio Press
The original T113 bore some resemblance to the T113E1 and E2. The new vehicle had a much sharper front with a full-size trim-vane and the trailing idler had been replaced with a new separate raised idler instead. The engine had changed too. Gone was the AOSI-314-2 air-cooled engine and X-drive transmission, replaced with a new 215hp Chrysler V8 model 361B (later known as the 75M) water-cooled petrol engine with Allison TX200-2 transmission. Otherwise, the large box body shape had not changed much.
The driver for this vehicle was stationed in the front left with the commander behind the driver and located centrally under a small roof hatch. A single .30 cal. machine-gun was fitted to a ring on the commander’s hatch.
The troop capacity had changed though. Originally it had been for 10 men, then changed to 13 and lastly, after modifications, it was just 11 men. These were to be seated on simple folding benches located in the back which accommodated 5 men each, sat in the back, on top of the thinned sponsons over the tracks facing inwards, and the 11th man sat in a folding seat directly behind the M113 commander facing backwards towards the ramp at the rear of the vehicle. The entire vehicle was 105 ¾” (2.69m) wide with the mudguards, which were removable reducing the width to exactly 100” (2.54m). It was 191 ½” long (4.86m) and the height to the top of the machine-gun was 98 ¼” (2.5 m), but could be reduced to 73 ½” (1.87m) for transport if required by removing it.
The Serialised Armored Personnel Carrier M113. Illustrated by Tank Encylopedia’s own David Bocquelet.
Testing and Approval
Testing of the T113E2 was completed in a remarkably short time. By January 1959, CONARC announced that they were satisfied that this ‘heavy’ version could meet all of their requirements as long as an additional 400lbs (181 kg) could be shed. Between a thinning of the floor and the bottom of the sponsons and rear hull, the required weight savings were made and, as such, on 2nd April 1959, the M113 was officially born as ‘M113, Standard A’ and approved to replace the M59 as the primary armored personnel carrier (APC) for the US Army. Two further pilot vehicles were produced by FMC to meet the modified T113E2 standard and full official production began by FMC in January 1960. By the time production ended in 1968, 14,813 M113s had been built, of which 4,974 were used by the United States and 9,839 were sold or given by military aid to other countries.
Production M113 with trim vane extended. Photo: Presidio Press.
The basic vehicle body for what was to become the M113 was fully welded ‘5083 aluminium’, 1 ½” (38mm) thick across the roof and thicker on the sides (1 ¾” – 44.5mm) and front 1 ½” (38mm). The floor was just 1 ⅛” thick (28.6mm) and, post-T113E2 lightening, the weight was 18,600lbs (8.44 tonnes) empty and 22,900lbs (10.39 tonnes) combat laden.
Suspension and performance
The running gear consisted of 5 road wheels on each side connected to torsion bar suspension running on a single-pin, center-guide, rubber-padded track 15” (381mm) wide. With the 215hp 75M engine, the M113 could reach a top speed of 40mph (64.4 km/h) on a hard surface. There were no water jets even though the vehicle was amphibious. With the trim vane extended, the M113 could propel itself by its tracks through water at 3 ½ mph (5.6 km/h), meaning it was only suitable for crossing small areas of relatively calm or slow moving water.
Dimensions and layout of M113. Photo: Presidio Press
The M113 had had a remarkably short development time for an armored vehicle which was to form the mainstay of personnel carriage in the US Army. It had met the requirements for cost, simplicity and, most of all, weight. These savings were not without a price though. From the start of production in 1960, the M113 was to undergo a multitude of improvements over its life to address some of these fundamental compromises from its development. As would become apparent later in its service life, the decision to find this weight saving by reducing the protection in the floor was to have dire consequences when the M113 was eventually used in Vietnam.
Links & Rources
Bradley: A history of American fighting and support vehicles. (1999) R.P. Hunnicutt, Presidio Press
Evaluation of one T113 and one T117 Universal Carrier Hull Against Combat Attack (U). (1959). W. B. Frye. Aberdeen Proving Ground, Maryland.
Dynamic Human Engineering Evaluation of the Armored Personnel Carriers T113 and T117. (1958). James Torre, Georges Garinther. Human Engineering Laboratory, APG
Osprey Publishing, New Vanguard #252: M113 APC 1960-75, Steven J. Zaloga