The squadron was first activated at MacDill Field, Florida in December 1942 as the 552d Bombardment Squadron, one of the four original squadrons of the 386th Bombardment Group.
 After training at MacDill and Lake Charles Army Air Field, Louisiana with the Martin B-26 Marauder, it departed for the European Theater of Operations in early May 1943.
 The ground echelon sailed on the RMS Queen Elizabeth on 27 May, while the air echelon ferried their Marauders to Europe via both the North Atlantic and South Atlantic ferry routes.

Upon arrival in England, the squadron was stationed at RAF Snetterton Heath.
 However, Eighth Air Force had decided to transfer its B-26 units from VIII Bomber Command to VIII Air Support Command and move them to stations closer to the European continent, so a week after its arrival, the squadron moved to RAF Boxted.
 This move also put the squadron's base in an area where it was planned to locate a future tactical air force.
 The squadron's entry into combat was delayed by the fact that its training in the United States had concentrated on low level attacks, while Eighth Air Force had determined to use the Marauders in medium level attacks to avoid light flak.
 This required additional training.
 Although some diversionary missions were flown, the squadron did not fly its first combat mission, an attack on Woensdrecht Airfield, until 30 July.

During its first month of combat the squadron concentrated on attacks on enemy air bases, although it also attacked gun positions and marshalling yards.
 In an effort to improve accuracy, the squadron participated in the 386th Group's first use of "drop on leader" tactics and revised formations in the European Theater on 2 September.
 The following month, the squadron flew its last mission with Eighth Air Force on 8 October when it attacked an airfield near Lille.

Shortly after its transfer to Ninth Air Force, the squadron began participating in an extensive campaign against V-1 flying bomb and V-2 rocket sites in Operation Crossbow.
 During Big Week, the squadron attacked airfields in Belgium and the Netherlands to weaken enemy air defenses against the heavy bombers striking the German aircraft industry in Operation Pointblank.
 In preparation for Operation Overlord, the invasion of the continent, it attacked airfields, marshalling yards and gun positions.
 In late May, just before the landings, it concentrated on bombing bridges across the Seine to interfere with possible enemy reinforcement of the landing areas.
 On D-Day it hit coastal defenses, and during the fighting in Normandy, struck fuel and supply depots, lines of communication and enemy positions.

The squadron provided air support for Allied forces attacking Caen and on 25 July supported Operation Cobra, the breakout at Saint Lo.
 For its efforts against enemy opposition since entering combat the previous summer, the squadron was awarded the Distinguished Unit Citation.
 During August, the squadron supported ground forces closing the Falaise gap to prevent surrounded German forces from escaping.
 September saw the squadron conducting attacks in the area of Brest.

In October, the squadron moved to Beaumont-sur-Oise Airfield, an advanced landing ground in France to be closer to allied forces advancing through northern Europe.
 From its location on the continent, it attacked Metz, targets in the Netherlands, and depots and defended areas in Germany.
 During the Battle of the Bulge in December 1944 and January 1945, it concentrated on attacks on bridges.

Shortly after the fighting in the Ardennes, the squadron was withdrawn from combat to convert from the Marauder to the Douglas A-26 Invader.
 It flew missions with its new plane from Sint-Truiden Airfield, Belgium through May 1945.
 The squadron's last mission was on 3 May, an attack on the Stod Ammunition Plant in Czechoslovakia.
 After V-E Day the squadron remained in Belgium until July, when it returned to the United States, inactivating at Westover Field, Massachusetts on 7 November 1945.
The squadron was first activated at MacDill Field, Florida in December 1942 as the 552d Bombardment Squadron, one of the four original squadrons of the 386th Bombardment Group.  After training at MacDill and Lake Charles Army Air Field, Louisiana with the Martin B-26 Marauder, it departed for the European Theater of Operations in early May 1943.  The ground echelon sailed on the RMS Queen Elizabeth on 27 May, while the air echelon ferried their Marauders to Europe via both the North Atlantic and South Atlantic ferry routes.
Upon arrival in England, the squadron was stationed at RAF Snetterton Heath.  However, Eighth Air Force had decided to transfer its B-26 units from VIII Bomber Command to VIII Air Support Command and move them to stations closer to the European continent, so a week after its arrival, the squadron moved to RAF Boxted.  This move also put the squadron's base in an area where it was planned to locate a future tactical air force.  The squadron's entry into combat was delayed by the fact that its training in the United States had concentrated on low level attacks, while Eighth Air Force had determined to use the Marauders in medium level attacks to avoid light flak.  This required additional training.  Although some diversionary missions were flown, the squadron did not fly its first combat mission, an attack on Woensdrecht Airfield, until 30 July.
During its first month of combat the squadron concentrated on attacks on enemy air bases, although it also attacked gun positions and marshalling yards.  In an effort to improve accuracy, the squadron participated in the 386th Group's first use of "drop on leader" tactics and revised formations in the European Theater on 2 September.  The following month, the squadron flew its last mission with Eighth Air Force on 8 October when it attacked an airfield near Lille.
Shortly after its transfer to Ninth Air Force, the squadron began participating in an extensive campaign against V-1 flying bomb and V-2 rocket sites in Operation Crossbow.  During Big Week, the squadron attacked airfields in Belgium and the Netherlands to weaken enemy air defenses against the heavy bombers striking the German aircraft industry in Operation Pointblank.  In preparation for Operation Overlord, the invasion of the continent, it attacked airfields, marshalling yards and gun positions.  In late May, just before the landings, it concentrated on bombing bridges across the Seine to interfere with possible enemy reinforcement of the landing areas.  On D-Day it hit coastal defenses, and during the fighting in Normandy, struck fuel and supply depots, lines of communication and enemy positions.
The squadron provided air support for Allied forces attacking Caen and on 25 July supported Operation Cobra, the breakout at Saint Lo.  For its efforts against enemy opposition since entering combat the previous summer, the squadron was awarded the Distinguished Unit Citation.  During August, the squadron supported ground forces closing the Falaise gap to prevent surrounded German forces from escaping.  September saw the squadron conducting attacks in the area of Brest.
In October, the squadron moved to Beaumont-sur-Oise Airfield, an advanced landing ground in France to be closer to allied forces advancing through northern Europe.  From its location on the continent, it attacked Metz, targets in the Netherlands, and depots and defended areas in Germany.  During the Battle of the Bulge in December 1944 and January 1945, it concentrated on attacks on bridges.
Shortly after the fighting in the Ardennes, the squadron was withdrawn from combat to convert from the Marauder to the Douglas A-26 Invader.  It flew missions with its new plane from Sint-Truiden Airfield, Belgium through May 1945.  The squadron's last mission was on 3 May, an attack on the Stod Ammunition Plant in Czechoslovakia.  After V-E Day the squadron remained in Belgium until July, when it returned to the United States, inactivating at Westover Field, Massachusetts on 7 November 1945.
552d Training Squadron