During the Battle of France, Simon led his regiment in the capture of Pixie, Lyon, Orléans, Tours and Bordeaux and then advanced to the border with Spain.

For the fighting in the Battles of the Demyansk Pocket, Simon was awarded the Knight's Cross and promoted to Oberführer (Senior Colonel).

In December 1942 Simon was promoted again to Brigadeführer (Brigadier General), prior to being given command of the SS Division Reichsführer-SS.

[2] In 1944, the division was moved to Italy, and fought, never complete, at Anzio and later in the Arno sector, where it gained a reputation for stability although it suffered heavy losses during the battles in the Apennines.

[3] The XIII SS Corps deployed to the Lorraine region against the United States Army, and from December 1944 defended the Siegfried Line.

The XIII SS Army Corps retreated into the Saarland and the Palatinate where it started to destroy the Rhine bridges.

In April 1945 between Main and Jagst it came up against the 4th US Armored Division and took part in heavy fighting around the Tauber – Colombia line and around Würzburg and Nuremberg.

On the orders of Simon the bridges over the Isar approaching Austria were not blown up, as he believed there was no need as the end of the war was near.

Even in death, Simon caused some controversy, as HIAG, an organization of former Waffen-SS members, attempted to place a glorifying obituary for him in the German newspaper Frankfurter Allgemeine.