During World War II the group was an Eighth Air Force fighter unit stationed in England. Assigned to RAF Martlesham Heath in 1943. Despite excellent leadership had highest ratio of losses to enemy aircraft claims of all Eighth Air Force fighter groups. It earned a Distinguished Unit Citation for actions on 17, 18, and 23 September 1944 for support of Operation Market-Garden airborne forces in the Netherlands.
Organized and trained in the Northeast United States by First Air Force. During training was part of the air defense of the northeast, being attached to the New York and Boston Fighter Wings.
Deployed to England aboard the RMS Queen Elizabeth and served in combat as part of VIII Fighter Command from October 1943 to May 1945, participating in operations that prepared for the invasion of the Continent, and supporting the landings in Normandy and the subsequent Allied drive across France and Germany. The group flew P-47 Thunderbolts until they were replaced by P-51 Mustangs in November 1944. Aircraft of the 356th were identified by a magenta/blue diamond pattern around their cowling.
From October 1943 until January 1944, operated as escort for B-17 Flying Fortress/B-24 Liberator bombers that attacked such objectives as industrial areas, missile sites, airfields, and communications.
Fighters from the 356th engaged primarily in bombing and strafing missions after 3 January 1944, with its targets including U-boat installations, barges, shipyards, aerodromes, hangars, marshalling yards, locomotives, trucks, oil facilities, flak towers, and radar stations. Bombed and strafed in the Arnhem area on 17, 18, and 23 September 1944 to neutralize enemy gun emplacements, and received a Distinguished Unit Citation for this contribution to the airborne attack on the Netherlands.
In early 1945, group's P-51 Mustangs clashed with German Me 262 jet aircraft. The group flew its last combat mission, escorting B-17's dropping propaganda leaflets, on 7 May 1945. It returned to Camp KilmerNew Jersey and was inactivated on 10 November 1945.