Armored infantry vehicle T59, T73, M59
A LOWER COST ARMORED PERSONNEL CARRIER
It also was desirable to consider a less expensive version of the armored infantry vehicle T18E1 (M75) then in production, in response to a verbal request from the Assistant Chief of Staff, G4, a work directive, dated 3 January 1952, was issued to complete the three remaining T18Els under production order T-24478 as lower cost vehicles.
Built by the International Harvester Company, they were subsequently designated as the armored infantry vehicle T73. The cost reduction was achieved by using a less expensive version of the Continental AO-895-4 engine, the Allison XT-500 transmission, and a modified hull structure.
The T73 retained the T18E1's homogeneous steel armor5/8inches thick on the front, sides, and rear. The top and floor were still 1/2 and 1 inch thick respectively. The driver rode in the left front above the sponson alongside the engine compartment.
Four periscopes were installed around his hatch. The vehicle commander was in the left center under a cupola with six vision blocks and an external mount for a .50 caliber machine gun. The personnel compartment seated ten infantrymen on two folding benches along the side walls. A single large door in the rear with a pistol port provided access to the vehicle.
Two roof doors could be opened for loading cargo or to permit the troops to fire from the vehicle. With the roof doors locked in the open position, a six inch firing space remained between the bottom of the doors and the hull roof.
The T73, with its 375 gross horsepower AO-895-4 engine had a gross power to weight ratio of 18.5 horsepower per ton compared to the 13.7 horsepower per ton for the T59 and 18.4 horsepower per ton for the T59E1.
However, it was not amphibious and access from the rear was limited to the single door unlike the ramp which opened the entire rear of the T59 and T59E1. The latter vehicles also were much quieter in operation.
After service tests, the Army selected the T59 as the new armored infantry vehicle and further development of the T73 was canceled. On 24 May 1953, the Assistant Chief of Staff, G4, directed that the armored infantry vehicle M59 (T59) be classified as standard and the armored infantry vehicle M75 (T18E1) also be retained as standard.
A contract was awarded to FMC Corporation for production of the M59 which sub-sequently was designated as the armored personnel carrier M59. The first production configuration vehicle was delivered in August 1953. The initial contract was for 2,385 M59s, but over 6,300 were produced by the time production ended in 1960.
The production M59 differed from the pilots by the installation of an escape hatch door in the rear ramp. The small vision port in the ramp was shifted to one side of the door. This door was installed in vehicles F7 - F31 and F41 up. M59s F32 - F40 replaced the escape hatch door with a small rectangular escape hatch.
The vision port on these vehicles was moved back to the top center of the ramp. This vision port was eliminated on the later production vehicles. The roof of the personnel compartment consisted of two hatches (one front and one rear) bolted to the hull.
Since they were hinged to each other, either hatch could be unbolted and folded on top of the other to permit loading of cargo. The front hatch had a door on the left side and the rear hatch had one on the right.(U.S. Army)
The production vehicles were fitted with a redesigned, manually operated, trim vane. The control handle for the trim vane was on the outside upper front armor within reach of either the driver or the vehicle commander. The GMC Model 302 engines were coupled to Model 300MG Hydramatic transmissions in vehicles F7 - F590.
In M59s F591 up, Hydramatic transmissions Model 30IMG were installed. These transmissions had four automatic forward and one reverse speeds which were transmitted through two differential speed ranges,a high range and a low range. The driver's shift lever was used to control both the transmission and the differential. In addition to neutral, there were three transmission ranges in both the high and low differential ranges.
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