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Mack Military - When Mack Trucks produced half-tracks (actually ¾ tracks) for Uncle Sam


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What didn’t Mack Trucks design and produce? While many are aware of the company’s off-highway mining trucks, trailers, locomotives, diverse range of rail cars and the best fire apparatus in the business, few realize how involved Mack Trucks once was with the United States military. Again and again, the U.S. Army turned to the engineering expertise of Mack Trucks for some of its most challenging projects.

Previously, I mentioned the little known but extremely impressive post-WW2 Mack T54 five-ton tactical cargo truck (http://www.bigmacktrucks.com/index.php?/topic/15604-mack-military-truck/page-3). Today I’d like to introduce you to the Mack half-tracks.

Ordered by the U.S. Army from Mack Trucks in December 1940, Mack Trucks’ T1 and T3 "three-quarter track” trucks were the result of a U.S. Army Ordinance Committee proposal calling for longer tracks than the M2/M3 half-tracks then in service to achieve the enhanced mobility necessary for pulling the army’s 105mm howitzer cross country.

Delivered to the army in October 1941, the Mack T3 with its advanced raked superstructure was the first "three-quarter track” truck produced by a U.S. manufacturer. Unlike the army’s M2 and M3 conventional “half-tracks”, Mack’s three quarter track design was far less likely to get stuck.

For standardization purposes, the Mack T3 utilized the rear suspension (vertical volute spring) and track assembly as the M2 light tank. Power from the 192 horsepower Mack EY707 engine (with twin carburetors) was directed thru a mid-ship mounted five-speed transmission and two-speed auxiliary transmission. A front-mounted winch was rated at 14 tons. The T3 weighed in at 20,720 pounds.

(When BMT allows me to post pictures once more, I'll add the supporting photographs. I apologize for the inconvenience)

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The Mack T1 was an experimental gun motor carriage featuring the 40mm Bofors semi-automatic anti-aircraft gun. Built in 1941, the T1 utilized Mack’s T3 three-quarter track platform. As a pre-production prototype, no armor was installed. The Mack T1 was well liked but the Army was frustrated with the Swedish gun*.

(Note the Mack Trucks vehicle identification plate on the right side of the steering column)

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* In order to supply both the Army and Navy with much greater numbers of the guns, Chrysler built 60,000 Bofors guns and 120,000 barrels through the war, at half the original projected cost, and filled the Army's needs by 1943. Chrysler engineers introduced numerous changes to improve mass production, eventually reducing the overall time needed to build a gun by half. Most of these changes were in production methods rather than the design of the gun itself.

There were many difficulties in producing the Bofors guns within the United States, beyond their complexity (illustrated by the use of 2,000 sub-contractors in 330 cities and 12 Chrysler factories to make and assemble the parts). The drawings were in metric, in Swedish and read from the first angle of projection, with lower precision than needed for mass production. Chrysler had to translate to English, fix absolute dimensions, and switch to the third angle of projection.

The U.S. Navy considered the original Bofors Model 1936 design to be completely unsuitable for the mass production techniques required to meet its needs. Firstly, the Swedish Bofors guns were designed using metric measurement units, a system all but unknown in the USA at that time. And often, the dimensions on the Swedish drawings didn’t match the actual measurements taken from the weapons. The Swedish Bofors gun also required a great deal of hand work in order to make the finished weapon. For example, Swedish blueprints had many notes on them such as "file to fit at assembly" and "drill to fit at assembly," all of which took much production time in order to implement. Thirdly, the Swedish gun mountings were manually operated, while the U.S. Navy required power-operated mountings in order to attain the fast elevation and training speeds necessary for engaging modern aircraft. Another concern was the Bofors guns being air-cooled, thus limiting their ability to fire long bursts, a necessity for most naval anti-aircraft engagements. And finally, the navy rejected the Swedish ammunition design. Deeming it not to be bore safe, the fuse was found to be too sensitive for normal shipboard use and its overall design was determined to be unsuitable for mass production. US manufacturers made radical changes to the Swedish design in order to minimize these problems. As a result, the Bofors guns and mountings produced in the United States bore little resemblance their Swedish ancestors.

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Ordered by the U.S. Army in 1942 (under contract W-670-ORD-2159), Mack Trucks delivered the first prototype T19 in November 1942 (USA W4015647) and the second in April 1943 (USA W4015648).

The T19 had a rear mounted 572 cubic inch 215 horsepower Continental R6572 engine (same as the M5 high-speed tractor) paired with a Mack synchronized four-speed transmission and two-speed transfer case.

The Mack T19 was designed to transport 14 soldiers as an armored personnel carrier (APC), or tow the army’s 105mm howitzer with its gun crew and ammunition, at speeds up to 38 miles per hour.

The Mack T19 was also test-mounted with the army’s 81mm mortar.

With ¼” thick hull armor, the Mack T19 weighed in at 23,292 pounds (combat loaded at 28,800 pounds).

The mounting arrangement for the 15-ton front winch was a brilliant example of Mack engineering. Positioned off-center, the winch was concealed within the front armor by a lift-up cover rather than mounted on the front bumper. This novel mounting arrangement improved the vehicle’s approach angle while reducing overall length.

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The Mack TrucksT1 experimental gun motor carriage

(Note the Mack Trucks vehicle identification plate on the right side of the steering column in the second photograph)

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post-16320-0-55820500-1381882008_thumb.j

post-16320-0-63029200-1381882022_thumb.j

Edited by kscarbel2
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Production continued, under the supervision of the Office of Production Management (later replaced by the War Production Board).

For example, the government ordered 80 huge FC and NW off-highway dump trucks in 1941 for use in expansion of the Panama Canal, a vital sea link for America's national defense.

Mack did continue to build some conventional buses and trolley buses until early 1943 for essential use.

And Mack continued to produce fire trucks for both civilian use and the military (though final assembly shifted from Allentown to Mack's plant in Long Island City, New York)

Mack built aircraft components for BT13 trainers and B-24 bombers.

Mack's transmission plant in New Brunswick, New Jersey produced tank transmissions.

The Mack bus plant in Allentown (5C) was requisitioned for production of Consolidated Vultee TBY "Seawolf" torpedo bombers for the navy.

Speaking of military production, Mack Trucks produced over 30,000 vehicles for the United States military and allied nations during World War II.

In 1942, the War Department presented Mack Trucks with the Army-Navy "E" Award for excellence, in recognition of the company's high achievement in the production of war materials.

Mack Trucks also received the National Security Award friom the Office of Civilian Defense for its successful programs protecting employees, plants and production from fire, explosion, air raids, accidents and other emergencies.

The U.S. Navy assigned Mack Trucks the task of designing a 400 horsepower supercharged V-12 diesel engine. Mack used a patented welded engine block design to meet the navy's requirement for this experimental engine.

Speaking of another instance when the military turned to Mack Trucks for its most challenging requirements, the company In 1945 presented the U.S. Army with the T8E1 doubled-ended tank transporter.

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