The Sixth Army saw extensive service in the South Pacific during World War II, including in New Britain, New Guinea, and the Philippines.

The first iteration of the Sixth Army was authorized by the National Defense Act of 1920 and was originally to be composed of Organized Reserve units primarily from the Seventh, Eighth, and Ninth Corps Areas.

[2] Under the code name Alamo Force,[3] it assumed control of the majority of US Army units involved in Operation Cartwheel, the campaign to isolate and neutralize the Japanese base at Rabaul in New Britain.

[4] Similar in conception to the island hopping operations of the central Pacific, the object of the attacks was to land, establish a garrison and airfield which could support the next strike, and then move on.

[5] As a prelude to that invasion, the island of Mindoro was invaded by the Western Visayan Task Force comprising the 19th and 503rd Regimental Combat Teams.

Sixth Army then continued to clear the north of Luzon and confronted the Shimbu Group in the Sierra Madres until the end of the war.