The unit was constituted as the 370th Fighter Group in May 1943, and activated on 1 July 1943 at Westover Field, Massachusetts.
The original squadrons of the group were the 401st, 402d and 485th Fighter Squadrons.

The group trained with Republic P-47 Thunderbolts at several First Air Force bases in New England then was deployed to RAF Aldermaston England during January and February 1944.
In Europe, it became an element of Ninth Air Force.

When the group arrived, the expected to receive Thunderbolts on which they had trained stateside.
However, much to the amazement of the Group Commander, Colonel Howard F. Nichols, the 370th FG was informed by IX Fighter Command that it would be equipped with the Lockheed P-38 Lightning, a few of which had already arrived during the 18 days the group was in residence at Aldermaston.
The latter base proved to be only a temporary station, as it was required for troop carrier operations; the 370th soon moved to RAF Andover.

From England, the group dive-bombed radar installations and flak towers, and escorted bombers that attacked bridges and marshalling yards in France as the Allies prepared for Operation Overlord, the invasion of the continent of Europe.
The group provided cover for Allied forces that crossed the Channel on D-Day, and flew armed reconnaissance missions over the Cotentin Peninsula until the end of the month.
On 17 July 1944, napalm incendiary bombs were dropped for the first time in war by 14 P-38 aircraft of the 402nd Fighter Squadron, led by 370th Group commander Col Nichols, on a fuel depot at Coutances, near St. Lô, France.

The group transferred to IX Tactical Air Command and moved the Advanced Landing Ground at Cardonville, France on 24 July to support the Allied ground advance across France and into Germany.
The 370th's fighter-bombers hit hard.
German Field Marshal von Kluge soon found that his armored forces moving towards Normandy were constantly beset by Allied fighter-bomber attacks.
Von Kluge phoned General Walter Warlimont, Hitler's personal representative on the Western front, "The enemy air superiority is terrific and smothers almost every one of our movements...Every movement of the enemy is prepared and protected by its air force.
Losses in men and equipment are extraordinary."
Von Kluge himself was not immune to personal danger.
USAAF Group Commander Nichols and a squadron of his P-38 Lightnings blasted von Kluge's own headquarters; the group commander himself skipped a 500-pound bomb right through the front door.
Moving across France, the 370th FG hit gun emplacements, troops, supply dumps, and tanks near Saint-Lô in July and in the Falaise–Argentan area in August 1944.

In September 1944, the group sent planes and pilots to England to provide cover for Operation Market-Garden, the allied airborne assault on the Netherlands and Germany.
The P-38s of the group struck pillboxes and troops early in October to aid First Army's capture of Aachen, and afterward struck railroads, bridges, viaducts, and tunnels in that area.

The 370th received a Distinguished Unit Citation for a mission in support of ground forces in the Hurtgen Forest area on 2 December 1944 when, despite bad weather and barrages of antiaircraft and small-arms fire, the group dropped napalm bombs on a heavily defended position in Bergstein, setting fire to the village and inflicting heavy casualties on enemy troops defending the area.
The 370th later flew armed reconnaissance during the Battle of the Bulge, attacking warehouses, highways, railroads, motor transports, and other targets.

The group converted to North American P-51 Mustangs during February – March 1945.
It bombed bridges and docks in the vicinity of Wesel to prepare for the crossing of the Rhine, and patrolled the area as paratroops were dropped on the east bank on 24 March Supported operations of 2d Armored Division in the Ruhr Valley in April.
 The group flew its last mission, a sweep over Dessau and Wittenberg, on 4 May 1945.

The 370th FG returned to the United States during September–November 1945, and was inactivated on 7 Novemb
The unit was constituted as the 370th Fighter Group in May 1943, and activated on 1 July 1943 at Westover Field, Massachusetts. The original squadrons of the group were the 401st, 402d and 485th Fighter Squadrons.
The group trained with Republic P-47 Thunderbolts at several First Air Force bases in New England then was deployed to RAF Aldermaston England during January and February 1944. In Europe, it became an element of Ninth Air Force.
When the group arrived, the expected to receive Thunderbolts on which they had trained stateside. However, much to the amazement of the Group Commander, Colonel Howard F. Nichols, the 370th FG was informed by IX Fighter Command that it would be equipped with the Lockheed P-38 Lightning, a few of which had already arrived during the 18 days the group was in residence at Aldermaston. The latter base proved to be only a temporary station, as it was required for troop carrier operations; the 370th soon moved to RAF Andover.
From England, the group dive-bombed radar installations and flak towers, and escorted bombers that attacked bridges and marshalling yards in France as the Allies prepared for Operation Overlord, the invasion of the continent of Europe. The group provided cover for Allied forces that crossed the Channel on D-Day, and flew armed reconnaissance missions over the Cotentin Peninsula until the end of the month. On 17 July 1944, napalm incendiary bombs were dropped for the first time in war by 14 P-38 aircraft of the 402nd Fighter Squadron, led by 370th Group commander Col Nichols, on a fuel depot at Coutances, near St. Lô, France.
The group transferred to IX Tactical Air Command and moved the Advanced Landing Ground at Cardonville, France on 24 July to support the Allied ground advance across France and into Germany. The 370th's fighter-bombers hit hard. German Field Marshal von Kluge soon found that his armored forces moving towards Normandy were constantly beset by Allied fighter-bomber attacks. Von Kluge phoned General Walter Warlimont, Hitler's personal representative on the Western front, "The enemy air superiority is terrific and smothers almost every one of our movements...Every movement of the enemy is prepared and protected by its air force. Losses in men and equipment are extraordinary." Von Kluge himself was not immune to personal danger. USAAF Group Commander Nichols and a squadron of his P-38 Lightnings blasted von Kluge's own headquarters; the group commander himself skipped a 500-pound bomb right through the front door. Moving across France, the 370th FG hit gun emplacements, troops, supply dumps, and tanks near Saint-Lô in July and in the Falaise–Argentan area in August 1944.
In September 1944, the group sent planes and pilots to England to provide cover for Operation Market-Garden, the allied airborne assault on the Netherlands and Germany. The P-38s of the group struck pillboxes and troops early in October to aid First Army's capture of Aachen, and afterward struck railroads, bridges, viaducts, and tunnels in that area.
The 370th received a Distinguished Unit Citation for a mission in support of ground forces in the Hurtgen Forest area on 2 December 1944 when, despite bad weather and barrages of antiaircraft and small-arms fire, the group dropped napalm bombs on a heavily defended position in Bergstein, setting fire to the village and inflicting heavy casualties on enemy troops defending the area. The 370th later flew armed reconnaissance during the Battle of the Bulge, attacking warehouses, highways, railroads, motor transports, and other targets.
The group converted to North American P-51 Mustangs during February – March 1945. It bombed bridges and docks in the vicinity of Wesel to prepare for the crossing of the Rhine, and patrolled the area as paratroops were dropped on the east bank on 24 March Supported operations of 2d Armored Division in the Ruhr Valley in April.  The group flew its last mission, a sweep over Dessau and Wittenberg, on 4 May 1945.
The 370th FG returned to the United States during September–November 1945, and was inactivated on 7 Novemb
140th Operations Group