The 99th Infantry Division was activated as a component of the Army of the United States on November 15th, 1942, with Headquarters at Camp Van Dorn, Mississippi. After participating in the 1943 Louisiana maneuvers, the Division had one change of station before embarking for the European Theater in September 1944. The 99th had a brief stop-over in England before landing at Le Havre, France, on November 3rd and proceeding to Aubel, Belgium, arriving on the front on November 9th north of the Roer River between Schmidt and Monshau, Germany. After a few weeks of intensive patrol action, the Division attacked the Westwall fortifications known as the Siegfried Line on December 13th and encountered strong enemy resistance.

On December 16th, the German Sixth Panzer Army hit the Division's lines in several place and made some breakthroughs in the opening attack of what would be called the Battle of the Bulge. Though facing numerically superior forces, the 99th held and withdrew gradually to defensive positions east of Elsenborn where the Divisions held in spite of enemy attempts to break through and enlarge the Bulge. After the German retreat from the Ardennes, the 99th re-equipped and engaged in aggressive patrol action until February 1, 1945, when it attacked enemy forces in the Monshau Forest area and continued to advance and mop up enemy remnants until February 13th. A rest and training period followed until March 2nd when the 99th advanced towards Keln, crossed the Erft Canal near Glesch, and then cleared several towns west of the Rhine.

On March 11th, the Division crossed the Rhine River at Remagen and advanced into the heart of Germany passing through Linz and crossing the Wied River on March 23rd. After cutting the Koln-Frankfurt Autobahn, the 99th crossed the Dill River and entered Giessen on March 29th and then moved to Schwarzenau to attack enemy forces trapped in the Ruhr Pocket. Advancing into the southeast sector of the pocket against fierce enemy resistance, the men of the 99th fought from April 5th until the 16th when Iserlohn was captured and organized enemy resistance ended. One week later, the Division was on the attack again and crossed the Ludwig Canal against strong enemy forces and advanced to the Altmuhl River which was crossed on April 25th.

Continuing to fight against die-hard enemy elements, the 99th crossed the Danube River near Eining on April 27th and crossed the Isar River four days later after a stubborn fight. The Division advanced to the Inn River and was at Giesenhausen east of Munich whe the war in Europe ended. After a short period of occupation duty, the Division returned home in September 1945 and was inactivated on October 15, 1945.

A total of 1,134 men of the "Checkerboard" Division were killed in action and 4,177 were wounded during three campaigns and 151 days of combat.

The shoulder patch worn by the 99th Division was approved on May 21, 1923. The black shield represents the iron district of Pennsylvania, and the checkerboard design is from the Coat of Arms of William Pitt.