It was the last United States field army to see service in northwestern Europe during the war and was commanded by General George S. Patton until his death in December 1945.

After World War II its mission was to carry out occupation duties and to gather historical information related to the European Theater of Operations.

The detachment proceeded to an estate called Doddington Hall in Cheshire, England, where they were billeted with XXII Corps which later came under operational control of Fifteenth Army.

Organization continued with a command post established at Chateau d'Ardennes although the main components of the Fifteenth remained in England.

As the German offensive now known as the Battle of the Bulge began, the CP was in danger and the headquarters evacuated to Cerfontaine, Belgium.

On December 25, 1944 the main body left Doddington Hall for a staging area in Southampton, England and boarded the British landing ship Empire Javelin the next afternoon.

It processed all new units which arrived at northern European ports through the staging areas until their 12th Army Group assignment.

Eighteen days later, the First and Ninth armies met at Paderborn, with Fifteenth holding the western side of the encirclement.

Fifteenth Army also turned east and assumed a defensive position (using XXII Corps) on the west bank of the Rhine from Bonn moving northeast toward Hamburg.

However, its formations did see some action, when it contained and then reduced the enormous Ruhr Pocket from the west during April 1945 in conjunction with elements of Ninth Army.

It took over responsibility for the Hesse, Saarland, Pfalz, and Rhine provinces, where it processed Axis POWs, Disarmed Enemy Forces and Displaced Persons.

Subsequently, the Fifteenth Army consisted solely of a small staff quartered at Bad Nauheim in the interior of Germany.

The Fifteenth Army was headquartered at Bad Neuenahr (within walking distance to Ahrweiler) beginning in late May 1945, according to the diary of one of the soldiers.

In his book General Ike: A Personal Reminiscence he writes[5] that one day in October 1945 'Ike' told him I had to fire George Patton today.