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The M7 (T26E4) snow tractor was standardized in August 1943, and was downgraded to Limited standard in November 1944. It was intended to pull a one-ton M19 snow trailer (T48). The tractor used many Allis Chalmers farm tractor components. It also used many Willys MB jeep powertrain components to lessen the military's spare parts inventory requirements.
The distinguishing feature of the M7 was the track system (halftrack). The M7's track ran on two rubber belts with four steel cables inside. The machine had a tendency to have the tracks come off in use. Another feature of both the tractor and trailer is that the tires could be switched with skis.
Prototyping of the machine that eventually became the M7 included several machines by Emmett Tucker (of subsequent Tucker Sno-Cat fame). At least one of the prototypes, a T26E3, still exists.
Something over ten percent of production, over 30 units, still survive. The track system and track plate width (18") look to have been borrowed from the early versions of the Weasel, although the M7 tracks are shorter with fewer plates.
M19 snow trailer
M19 1-ton snow trailer
Saginaw Products made the M19 ski-wheel trailers. Two production batches are known, one in 1944 and one in 1950.
The M19 trailer had a net weight of 640lbs, and a payload of 2,000lbs. It had a wooden body on a steel hollow-section frame, with hood, hoops, side and end panels all easily detachable, and it was normally equipped with a heater and two stretchers, plus a rear pintle hitch so that trailers could be doubled up. The two-bolt mounting pintle hitch was unique to the M7 and M19, and would not accommodate even an ordinary MB / GPW jeep trailer lunette.
They had three main functions;
Rescue and recovery, for which they were equipped with two stretchers and a personnel heater
Aircraft starting, for which they were outfitted with much larger aircraft engine heaters and slave power equipment
Cargo, for which they could be operated with or without canvas hood, top bows, side and end frames
Serial numbers for the 1950 units seem to start at 1,000 and were dated around November of that year, suggesting they were made to supplement a batch of 1944 originals that were going to Norway, and seem to top out around 1,150.
It is quite likely that the 1944 batch did not run to as much as 1,000 units, as 600 would have supplied two trailers for every M7 that Allis Chalmers built. Estimated total production would be around 750 ( 600 in 1944 and 150 in 1950 ) but many 1950 trailers seem to have survived due to careful use by the Norwegian Army.
The 1944 originals had several noted weak points which can all be attributed to the lightness of construction ( they were rated at 2,000lbs, same as a Ben Hur trailer, but weighed only one third as much - 640lbs )
The 1944 tow bar frames had holes for bolting through the drag chains - 1950 trailers had no holes and drag chain ends welded to the tow frame.
The 1944 skis were mostly wood / ply with metal brackets and strake - 1950 trailers had metal sheath underneath, with strake welded to it.
The 1944 front support legs were quite short - 1950 support legs were lengthened by a couple of inches.
The 1944 units came with ordinary MB / GPW split combat rims, 1950 units came with 15" solid rims, which were interchangeable and might have been from M series jeeps. (clarification needed)
In addition to those points they tried to recover as much weight as they could by lightening. The 1944 heavy rectangular bracket for mounting the heater was replaced by a much lighter flimsy unit on the 1950 production. The type of plug and socket for the lights and auxiliary power also looks to have been updated.
Despite this rework all M19s are very prone to damage. The trailer body will bend noticeably when loaded away from the axle line and normally stays out of flat. The tow frame is a fabrication work of art, being split, angled, and welded, but this results in a lot of work and since they appear not to have been coated internally when new, most are now quite weak as a result of internal rusting.
The canvas covers were insulated by quilting, and had one green side and one white side, plus flaps and reinforcement for the various heater and ventilation exhaust outputs - many of which were doubled to allow the covers to be reversible.
The low tow hitch position and small tow ring means they were really only suitable for towing behind an M7, as they dragged at quite an angle when hitched to a Weasel. An M7 tractor could tow two loaded M19 trailers on solid going such as an ice or snow-covered road, and when rougher ground was to be traversed it would drop one unit and shuttle them across the rougher ground one at a time.
A tractor is an engineering vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most commonly, the term is used to describe a farm vehicle that provides the power and traction to mechanize agricultural tasks, especially tillage, and now many more. Agricultural implements may be towed behind or mounted on the tractor, and the tractor may also provide a source of power if the implement is mechanised.
The three-point hitch is a widely used type of hitch for attaching ploughs and other implements to an agricultural or industrial tractor. The three points resemble either a triangle, or the letter A. In engineering terms, three-point attachment is the simplest and the only statically determinate way of rigidly joining two bodies.
A trailer is an unpowered vehicle towed by a powered vehicle. It is commonly used for the transport of goods and materials.
Allis-Chalmers was a U.S. manufacturer of machinery for various industries. Its business lines included agricultural equipment, construction equipment, power generation and power transmission equipment, and machinery for use in industrial settings such as factories, flour mills, sawmills, textile mills, steel mills, refineries, mines, and ore mills.
A tow hitch is a device attached to the chassis of a vehicle for towing, or a towbar to an aircraft nose gear. It can take the form of a tow ball to allow swiveling and articulation of a trailer, or a tow pin, or a tow hook with a trailer loop, often used for large or agricultural vehicles where slack in the pivot pin allows similar movements. Another category is the towing pintle used on military vehicles worldwide.
The M29 Weasel is a World War II tracked vehicle designed for operation in snow. Built by Studebaker, Weasels were also used in sandy, muddy, and desert terrains, including towing loads over terrain wheeled vehicles could not negotiate as in the U.S. Marine invasions of Iwo Jima and Okinawa.
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Towing is coupling two or more objects together so that they may be pulled by a designated power source or sources. The towing source may be a motorized land vehicle, vessel, animal, or human, and the load being anything that can be pulled. These may be joined by a chain, rope, bar, hitch, three-point, fifth wheel, coupling, drawbar, integrated platform, or other means of keeping the objects together while in motion.
The Commercial Utility Cargo Vehicle (CUCV) is a vehicle program instituted to provide the United States military with light utility vehicles based on civilian trucks.
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The All-Crop harvester or All-Crop combine was a tractor-drawn, PTO-driven combine harvesters made by Allis-Chalmers from the mid-1930s to the early 1960s. Aside from small grains, these harvesters were able to harvest some flowers, as well as various grasses and legume crops for seed.
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M1 Heavy Tractor was a term used by the United States Army during World War II for several different models of "off the shelf" civilian tracked tractors adopted for military use. Under the Ordnance Department, these tractors were meant to tow artillery pieces, and were not equipped with blades like their Corps of Engineers counterparts. Later in the war, these tractors were replaced in the prime mover role by heavy trucks such as the Mack NO or purpose-built "High Speed Tractors" such as the M4, M5, or M6. Some tractors were equipped with crane attachments for ammunition and material handling.
The 6-ton 6×6 truck was a family of heavy tactical trucks built for the United States Army during World War II. The basic cargo version was designed to transport a 6- short ton (5,400 kg) cargo load over all terrain in all weather. The chassis were built by Brockway Motor Company, The Corbitt Company, The Four Wheel Drive Auto Company (FWD), Ward LaFrance Truck Corporation, and White Motor Company. They were replaced by the M54 5-ton 6x6 trucks in the 1950s.
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