The squadron was first organized at Key Field, Mississippi in February 1943 as the 621st Bombardment Squadron, one of the four original squadrons of the 404th Bombardment Group.
 The squadron was initially equipped with a mix of Douglas A-24 Banshees and Bell P-39 Airacobras.
 In July 1943, the squadron moved to Congaree Army Air Field, South Carolina, where it was redesignated the 507th Fighter-Bomber Squadron The following month.
 In early 1944, the squadron converted to Republic P-47 Thunderbolts.
 Completing its training for combat in March, it deployed to the United Kingdom.

The squadron arrived at its first overseas station, RAF Winkton, England in early April.
 It became operational on 1 May and began bombing and strafing targets in France to help prepare for Operation Overlord, the invasion of Normandy.
 At the end of the month, it dropped the "Bomber" from its name and became the 507th Fighter Squadron, but retained the air support mission.
 The squadron provided top cover for the landings on D-Day.
 A month later, on 6 July, the squadron moved to Chippelle Airfield in France, from which it provided air support for Operation Cobra, the Allied breakout at Saint-Lô, later that month.
 Despite suffering heavy losses from flak, the squadron helped cover four armored divisions duging the breakout.
This support earned the squadron the French Croix de Guerre with Palm.

The squadron supported the Allied advance across the Netherlands, operating from bases in France and from Sint-Truiden Airfield, Belgium.
Its actions in this area, resulted in the squadron being cited in the order of the day of the Belgian Army and the award of the Belgian Fourragère for its contributions to the liberation of the Belgian people.
On 10 September, the squadron participated in three armed reconnaissance missions.
 On these missions, despite adverse weather and heavy antiaircraft fire, the squadron attacked lines of communications, factories and rail targets as ground forces advanced.
 These missions earned the squadron the Distinguished Unit Citation.

During December 1944 and January 1945, attacked German positions during the Battle of the Bulge.
 Later it supported Operation Lumberjack and the establishment of a bridgehead on the west bank of the Rhine in March 1945.
 The squadron also flew air interdiction missions, strafing and bombing troop concentrations, railroads, highways, bridges, ammunition and fuel dumps, armored vehicles, docks, and tunnels.
 It covered bombing missions by Boeing B-17 Flying Fortresses, Consolidated B-24 Liberators, and Martin B-26 Marauders.
On 4 May, the squadron flew armed reconnaissance missions that would prove to be its last combat missions of the war.

The squadron briefly served with occupation forces in Germany before returning to the United States in August 1945.
 It reassembled at Drew Field, Florida on 11 September, but was inactivated on 9 November 1945.
The squadron was first organized at Key Field, Mississippi in February 1943 as the 621st Bombardment Squadron, one of the four original squadrons of the 404th Bombardment Group.  The squadron was initially equipped with a mix of Douglas A-24 Banshees and Bell P-39 Airacobras.  In July 1943, the squadron moved to Congaree Army Air Field, South Carolina, where it was redesignated the 507th Fighter-Bomber Squadron The following month.  In early 1944, the squadron converted to Republic P-47 Thunderbolts.  Completing its training for combat in March, it deployed to the United Kingdom.
The squadron arrived at its first overseas station, RAF Winkton, England in early April.  It became operational on 1 May and began bombing and strafing targets in France to help prepare for Operation Overlord, the invasion of Normandy.  At the end of the month, it dropped the "Bomber" from its name and became the 507th Fighter Squadron, but retained the air support mission.  The squadron provided top cover for the landings on D-Day.  A month later, on 6 July, the squadron moved to Chippelle Airfield in France, from which it provided air support for Operation Cobra, the Allied breakout at Saint-Lô, later that month.  Despite suffering heavy losses from flak, the squadron helped cover four armored divisions duging the breakout. This support earned the squadron the French Croix de Guerre with Palm.
The squadron supported the Allied advance across the Netherlands, operating from bases in France and from Sint-Truiden Airfield, Belgium. Its actions in this area, resulted in the squadron being cited in the order of the day of the Belgian Army and the award of the Belgian Fourragère for its contributions to the liberation of the Belgian people. On 10 September, the squadron participated in three armed reconnaissance missions.  On these missions, despite adverse weather and heavy antiaircraft fire, the squadron attacked lines of communications, factories and rail targets as ground forces advanced.  These missions earned the squadron the Distinguished Unit Citation.
During December 1944 and January 1945, attacked German positions during the Battle of the Bulge.  Later it supported Operation Lumberjack and the establishment of a bridgehead on the west bank of the Rhine in March 1945.  The squadron also flew air interdiction missions, strafing and bombing troop concentrations, railroads, highways, bridges, ammunition and fuel dumps, armored vehicles, docks, and tunnels.  It covered bombing missions by Boeing B-17 Flying Fortresses, Consolidated B-24 Liberators, and Martin B-26 Marauders. On 4 May, the squadron flew armed reconnaissance missions that would prove to be its last combat missions of the war.
The squadron briefly served with occupation forces in Germany before returning to the United States in August 1945.  It reassembled at Drew Field, Florida on 11 September, but was inactivated on 9 November 1945.
188th Rescue Squadron