The group was first activated at Salt Lake City Army Air Base, Utah in September 1942, with the 502d, 503d, 504th and 505th Bombardment Squadrons assigned[1] The following month, it moved to Smoky Hill Army Air Field, Kansas, where it began operating as an Operational Training Unit (OTU).

[2] The Army Air Forces (AAF) OTU program involved the use of an oversized parent unit to provide cadres to "satellite groups".

[3] However, the AAF was finding that standard military units, based on relatively inflexible tables of organization were not well adapted to the training mission.

[4] The 346th Group and its squadrons were inactivated on 1 April 1944,[1][2] along with support organizations at Dyersburg Army Air Base, Tennessee, and replaced by the 223d AAF Base Unit (Combat Crew Training Station, Bombardment, Heavy) The group was reactivated at Dalhart Army Air Field, Texas in August 1944 as a very heavy bomber unit.

[6][7][8] The group trained with Boeing B-29 Superfortress at Dalhart and at Pratt Army Air Field, Kansas until late June 1945, when it departed the United States for the Pacific Theater.