In September it moved to Casper Army Air Field, where it conducted Boeing B-17 Flying Fortress replacement training until 1943, when it converted to the Consolidated B-24 Liberator.

[2] However, the Army Air Forces found that standard military units, based on relatively inflexible tables of organization, were not proving to be well adapted to the training mission.

It had all but the tail defensive armament removed, since experience had shown that by 1944 the only significant Japanese fighter attacks were coming from the rear.

The elimination of the turrets and the associated General Electric computerized gun system increased the top speed of the Superfortress to 364 mph at 25,000 feet and made the B-29B suitable for fast, unescorted hit-and-run bombing raids and photographic missions.

Flew first mission against the Japanese home islands on 9 July 1945 and afterward operated principally against the enemy's petroleum industry on Honshū.

Despite the hazards of bad weather, fighter attacks, and heavy flak, the 331st bombed the coal liquefaction plant at Ube, the Mitsubishi-Hayama petroleum complex at Kawasaki, and the oil refinery and storage facilities at Shimotsu, in July and August 1945, and received a Distinguished Unit Citation for the missions.