By June 1940 Congressional measures had augmented the federal budget for construction of arms and munitions plants, coastal defenses, and military training camps and expansion of existing bases.

Because Oklahoma's location, climate, natural resources, and large available work force were optimum, the War Department considered the state a good site for pilot and infantry training fields.

[4][5] Some of the farmers who had owned or worked the property were relocated by the Resettlement Administration, while others were forced to leave their farms within 45 days while crops were still growing.

The camp ultimately encompassed between 60,000 and 70,000 acres (240 and 280 km2) of eastern Oklahoma, or approximately 109 square miles (280 km2) of land lying east of the Arkansas River and State Highway 10 in Muskogee and Cherokee counties.

Manhattan-Long estimated that it needed to construct one new building every hour, in order to meet the deadline—no real feat, for on the Fort Riley, Kansas, job the company had built one every thirty-eight minutes.

The army also used preexisting buildings within the reservation boundary; a ranch house complex (built in 1936 by the Pray family) served as the post commander's billet.

This part of the facility served as an area for barracks, for general administration, for engineer, ordnance, maintenance, and chemical warfare operations, and for medical and hospital services.

During the course of World War II Camp Gruber provided training to infantry, field artillery, and tank destroyer units that went on to fight in Europe.

Adjacent to the main gate is a sheltered collection of ornate monuments crafted by the POWs, who also left their mark with post's network of brick-lined drainage canals, their continued hearty condition decades later being a testament to the Germans' engineering and workmanship.

Camp Gruber served as infantry and support group training base for the U.S. Army until after the end of World War II.