In 1940 Mack Trucks started the development of a wheeled artillery tractor for the U.S. Army, with an off-road payload of tons, to tow the 155 mm gun, the 8 inch howitzer, and the 240 mm howitzer. A contract for the production of the vehicle was awarded in September 1940, and in January 1942 a vehicle of the NO-1 type towed the first 240 mm howitzer carriage from the Bucyrus plant in South Milwaukee, Wisconsin to the Aberdeen Proving Ground test facility. The NO-1 was the first in a series of five very similar prime mover vehicles. The NO-2 differed in details, among them a canvas cabin roof and the winchbehind the front bumper. A total of 403 units of the NO-2 were delivered in 1943. The next prime mover models, which marginally differed from the NO-2, were the NO-3 and NO-6. A total of 1,097 units of these were ordered and delivered in 1943 and 1944. The last of the series was the NO−7 model, of which 188 were delivered in 1944 and 362 in 1945. Several NO-7 were provided after the war to the European armies being rebuilt, including those of United Kingdom, France, Belgium and Netherlands. The models NO-4 and NO-5 were prototypes of heavy salvage vehicles, equipped with a Gar Woodcrane which could swivel to the left and right. Neither model was put in production.
Description
The vehicle had a typical configuration, with a hoodedfront engine behind which was a large driver cabin that could seat five soldiers, and a rear cargo area. The engine was a Mack EY, 6-cylinder gasoline with a displacement of ; generating at 2100 rpm and at 800 rpm. The transmission had 5 gears forward and one reverse. The installation of a transfer case with an additional reduction gear allowed high and lowgearing. Traction was in all six wheels, with 14.00-24 tires. The empty weight of the vehicle was, and fully loaded. The gas tanks were located on both sides of the vehicle, with a total capacity of. At the front of the vehicle a Gar Wood winch was installed with a pulling capacity of. It could be used to assist in placing the gun, or to help moving the vehicle if it was stuck. The cargo area was long by wide and could carry tons of cargo. Starting with the NO-2 model, at the rear of the cargo compartment a small crane was installed to assist in placing the gun. The maximum towed load of the vehicle was 50,000 lb
Variants
In total 2,053 Mack NO vehicles were built, in 7 variants as described in the following table.
