The XII Corps fought from northern France to Austria in World War II. Constituted in the Organized Reserves in 1933, it was activated on 29 August 1942 at Columbia, South Carolina. XII Corps became operational in France as part of Lieutenant General George S. Patton's Third Army on 1 August 1944. Initially commanded by Major General Gilbert R. Cook, bad health forced MG Cook to relinquish command to Major General Manton S. Eddy within three weeks. MG Eddy commanded the corps until late April 1945, when his own health problems forced him to turn over command to MG Stafford LeRoy Irwin.
Pursuit across northern France
Assembling south of Le Mans on 13 August 1944, XII Corps began driving eastward and liberated the cities of Orléans and Châteaudun within five days. Moving rapidly against disorganized German resistance, the corps rapidly took Sens, Montargis, Troyes, Châlons-sur-Marne, and Vitry-le-François. By 31 August 1944, XII Corps had seized a bridgehead over the Meuse River at Commercy in Lorraine.
Lorraine
At the beginning of September 1944, serious gasoline shortages forced an abrupt halt to General Patton's pursuit across northern France. Resuming its advance on 4 September, but facing shortages of gasoline and ammunition because of the allied logistical crisis, XII Corps now confronted a vastly changed tactical situation. A combination of German reinforcements and regained cohesion in the German forces (5th Panzer Army) confronting the U.S. Third Army resulted in dramatically increased German resistance in the region of Metz and Nancy in the Moselle River valley. From the German point of view, Lorraine (German: Lothringen) was seen as part of Germany and would be defended with bitter determination.
Across the Moselle
XII Corps assaulted across the Moselle River at Dieulouard on 13 September 1944, and heavy fighting ensued for three days as the Germans attempted to collapse the bridgehead. During 15–16 September, the corps liberated Nancy and Lunéville. The advance of XII Corps was met by an armored counterattack of the 5th Panzer Army. At Arracourt during 19–20 September 1944, the corps' U.S. 4th Armored Division destroyed two German Panzer brigades. Desperate fighting continued until 1 October 1944 for the area around Arracourt, Moyenvic, and Grémecey's forest. Resuming its advance, the corps pushed to the river Seille by 9 October 1944.
To the Saar
After resting and reorganizing for a month, XII Corps opened an offensive to reach the Saar River on 8 November 1944. Château-Salins was taken on 9 November, and the corps battled through firm German resistance to liberate Faulquemont on 20 November 1944. On 24 November, the corps crossed the Sarre River and then liberated Saint-Avold on 27 November 1944. From 1 to 11 December 1944, XII Corps fought for, and liberated the towns of Sarre-Union and Sarreguemines. On 12 December, the corps entered Germany and began operations against the Siegfried Line fortifications.
Ardennes
Germany's surprise offensive into the Ardennes on 16 December 1944, resulted in the U.S. Third Army being moved northward to attack the southern flank of the German army in Belgium and Luxembourg. Turning over its part of the front to the U.S. XV Corps, XII Corps moved to the area of Luxembourg city on 21 December 1944. Subsequently, the corps cleared the west bank of the Moselle River in Luxembourg until 11 January 1945. During 18–23 January, XII Corps assaulted across the Sauer River and cleared the twin confluences of the Our River and the Sauer, and then that of the Sauer and Moselle Rivers.
Into Germany
On 7 February 1945, the corps assaulted across the Our and Sauer Rivers between Vianden and Echternach, repelling German counter-attacks against the bridgeheads and gradually clearing Siegfried Line bunkers in the area until 15 February. On 18 February 1945, XII Corps drove on the Prüm River, which it assaulted across on the night of 24–25 February. Bitburg fell to XII Corps on 28 February 1945. The corps assaulted across the Kyll River on the night of 2–3 March 1945, and reached the Rhine River in the area of Andernach on 7 March. From 7–11 March 1945, the corps mopped up along the west bank of the Rhine and Moselle Rivers.