Established as a Boeing B-29 Superfortress heavy bomb group in early 1944; trained under Second Air Force in Nebraska.

On 25 May 1945, the squadron flew a low-altitude night mission through alerted enemy defenses to drop incendiary bombs on Tokyo, for which they received their first Distinguished Unit Citation.

By mining harbors in Japan and Korea in July 1945, the squadron contributed to the blockade of the Japanese Empire earning their second Distinguished Unit Citation.

The 40th's final World War II mission came on 14 August 1945, with the dropping of 500-pound general-purpose bombs on the Marifu railroad yards at Iwakuni.

Continued strategic bombardment training until 1967 when the squadron was inactivated with the closing of Walker Air Force Base.