The prototype military 6x6 built by International Harvester bore little resemblance to the production vehicles which would follow. The prototype used what was apparently hand-crafted cab sheet metal, whereas the subsequent vehicles used an adaptation of International’s K-series civilian trucks.

The prototype military 6x6 built by International Harvester bore little resemblance to the production vehicles which would follow. The prototype used what was apparently hand-crafted cab sheet metal, whereas the subsequent vehicles used an adaptation of International’s K-series civilian trucks. 

United States purchase of International Harvester 6x6 trucks began in 1941 prior to the nation’s entry into WWII. The initial purchase included 500 M-5-6 cargo trucks (M= “military,” 5= “five thousand pound capacity,” and 6= “six-wheel drive”):

425 were short wheelbase without winch. 

25 were short wheelbase with winch, 

25 were long wheelbase without winch

25 were long wheelbase with winch.

Production of these vehicles was completed in 1942. Virtually all of these vehicles were shipped to the Soviet Union, as were some 3,000 long wheel base cargo trucks lacking the front axle drive. These latter trucks were designated the model M-5-6x4. All of the trucks supplied to Russia were closed-cabbed vehicles.

Ultimately adopted by the United States Marine Corps, the Internationals were fitted with a variety of beds. In addition to the standard cargo beds, International 6x6s were equipped as dump, pipeline, tanker, telephone and fire trucks. 

With the Army virtually monopolizing the production of GMC, Studebaker and Reo, the big corn binder soon came to the attention of the Navy Department. The flexibility of the Hendrickson suspension immediately caught the eye of the Marines.

With the Army virtually monopolizing the production of GMC, Studebaker and Reo, the big corn binder soon came to the attention of the Navy Department. The flexibility of the Hendrickson suspension immediately caught the eye of the Marines.

A truly rare vehicle is shown here. Only 25 M-5-6 trucks were built with short wheelbase, winch and closed cab. This one was photographed during testing at Ft. Holabird, Maryland, in May 1941.

A truly rare vehicle is shown here. Only 25 M-5-6 trucks were built with short wheelbase, winch and closed cab. This one was photographed during testing at Ft. Holabird, Maryland, in May 1941. 

Another scarce truck, a long wheelbase closed cab truck with winch. Only 50 long wheel base trucks were on the initial order, and only half of them were equipped with the front mounted PTO-driven winch exhibited on this truck.

Another scarce truck, a long wheelbase closed cab truck with winch. Only 50 long wheel base trucks were on the initial order, and only half of them were equipped with the front mounted PTO-driven winch exhibited on this truck. 

Typical of short wheelbase U.S. tactical vehicles of the time, the short M-5-6 had twin spare tires mounted behind the cab. The short wheelbase trucks were intended as artillery prime movers, and the dual spares could be added to the front axle for added traction when maneuvering in severe conditions.

Typical of short wheelbase U.S. tactical vehicles of the time, the short M-5-6 had twin spare tires mounted behind the cab. The short wheelbase trucks were intended as artillery prime movers, and the dual spares could be added to the front axle for added traction when maneuvering in severe conditions. 

Once it was decided that the standard Navy and Marine Corps 6x6 was to be the International, some changes were made, the model then becoming M-5H-6. The engine was upgraded to the 360.8 cubic inch FBC-361B, and the rear axles were equipped with Thornton self-locking differentials, and the tire size increased from the 7.50-20 tires previously used to 8.25-20 tires. The locking differentials provided the Internationals with off road performance superior to that of the CCKW or US6.

Once it was decided that the standard Navy and Marine Corps 6x6 was to be the International, some changes were made, the model then becoming M-5H-6. The engine was upgraded to the 360.8 cubic inch FBC-361B, and the rear axles were equipped with Thornton self-locking differentials, and the tire size increased from the 7.50-20 tires previously used to 8.25-20 tires. The locking differentials provided the Internationals with off road performance superior to that of the CCKW or US6. 

Whereas the M-5-6 used the standard cargo bed adopted by the army for GMC, Studebaker, etc., the Marines preferred something different for their M-5H-6. The bed shown here became standard on the International cargo trucks, with the spare tire mounted externally on the side of the body.

Whereas the M-5-6 used the standard cargo bed adopted by the Army for GMC, Studebaker, etc., the Marines preferred something different for their M-5H-6. The bed shown here became standard on the International cargo trucks, with the spare tire mounted externally on the side of the body. 

Pioneer tools were mounted on the forward outside portion of the cargo body on the driver's side. Notice also the fuel can and bracket mounted on the left front fender. Most of the USMC vehicles were equipped with a 10000-pound capacity PTO driven front winch and an open cab.

Pioneer tools were mounted on the forward outside portion of the cargo body on the driver's side. Notice also the fuel can and bracket mounted on the left front fender. Most of the USMC vehicles were equipped with a 10000-pound capacity PTO driven front winch and an open cab. 

Virtually anywhere the Marines go, the Seabees get there first. Not surprisingly then the M-5H-6 was also produced in a dump truck variant. Built on the short wheelbase chassis, these trucks and the larger 4-ton Diamond T were the two best dump trucks in the military’s inventory during WWII.

Virtually anywhere the Marines go, the Seabees get there first. Not surprisingly then the M-5H-6 was also produced in a dump truck variant. Built on the short wheelbase chassis, these trucks and the larger 4-ton Diamond T were the two best dump trucks in the military’s inventory during WWII.

The dump trucks were wisely equipped with steel cab protectors as shown here, but these were not always reinstalled after the trucks had been shipped into forward areas. Heavily laden and often operating in sand on Pacific Islands, the locking differentials proved worthy of their expense on these trucks.

The dump trucks were wisely equipped with steel cab protectors as shown here, but these were not always reinstalled after the trucks had been shipped into forward areas. Heavily laden and often operating in sand on Pacific Islands, the locking differentials proved worthy of their expense on these trucks.

Seabees leveling an airfield on Iwo Jima, June 1945

Seabees leveling an airfield on Iwo Jima, June 1945

As the standard chassis for the Marine Corps, the International was adapted for many of the same roles for which the Army used the CCKW. Among these was a basis for a tanker truck.

As the standard chassis for the Marine Corps, the International was adapted for many of the same roles for which the Army used the CCKW. Among these was a basis for a tanker truck.

Tractor versions of the International, like all the IH short wheelbase trucks had their fuel tanks mounted transversely behind the cab.

Tractor versions of the International, like all the IH short wheelbase trucks had their fuel tanks mounted transversely behind the cab. 

Like their GMC and Studebaker counterparts, the short wheelbase IH 2.5 ton trucks were intended for use as artillery prime movers as shown here.

Like their GMC and Studebaker counterparts, the short wheelbase IH 2.5 ton trucks were intended for use as artillery prime movers as shown here.

The Marines used the long wheelbase chassis for many purposes as well, including adaptation to fire trucks such as this one.

The Marines used the long wheelbase chassis for many purposes as well, including adaptation to fire trucks such as this one. 

One of the least documented uses of the short wheelbase International chassis was the wrecker variant shown here. These vehicles had a standard front mounted self-recovery winch, and a considerably more powerful gear driven winch behind the cab.

One of the least documented uses of the short wheelbase International chassis was the wrecker variant shown here. These vehicles had a standard front mounted self-recovery winch, and a considerably more powerful gear driven winch behind the cab. 

No doubt the most overburdened of the Internationals were the Navy’s mobile machine shop variants. These trucks were equipped with special bodies made by Couse which provide complete forward area repair and machining capabilities.

No doubt the most overburdened of the Internationals were the Navy’s mobile machine shop variants. These trucks were equipped with special bodies made by Couse which provide complete forward area repair and machining capabilities.

By the end of production, International built and delivered more than 30,000 of these trucks.

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