Following flight training, he was posted to Jagdgeschwader 134 "Horst Wessel" (JG 134—134th Fighter Wing) before World War II.

In late 1940, Simsch was transferred to Jagdgeschwader 52 (JG 52—52nd Fighter Wing) and fought against the Royal Air Force (RAF).

In November 1943, Simsch was transferred to Jagdgeschwader 11 (JG 11—11th Fighter Wing), a unit fighting in Defense of the Reich.

One week later, and two days after the Normandy landings, Simsch was shot down and killed in action on 8 June 1944 over Rennes, France.

[4] World War II in Europe began on Friday 1 September 1939 when German forces invaded Poland.

Due to adverse weather conditions, the attack was called off and only a Schwarm, a flight of four aircraft, under the leadership of Simsch, was assumed to have reached the target.

[6] The pilots Simsch, Feldwebel Georg Mayr, Gefreiter Adolf Glunz and Unteroffizier Hans Sembill were punished by Hermann Göring personally.

[7] According to Barbas, Simsch claimed an unconfirmed aerial victory over a RAF Supermarine Spitfire north of Dover on 19 May 1941.

Gruppe of JG 52, without a period of replenishment in Germany, was ordered to airfields close to the German-Soviet demarcation line.

Fliegerkorps commanded by Generaloberst Wolfram Freiherr von Richthofen which supported the northern wing of Army Group Centre.

Gruppe moved to an airfield at Klin, located 85 kilometers (53 mi) northwest of Moscow, on 30 November.

[23] On 3 November 1942, engine failure of his Bf 109 G-2 (Werknummer 13711—factory number) resulted in a forced landing northwest of Maykop.

[25] On 30 November 1943, following a lengthy period of convalescence, Simsch was transferred to Jagdgeschwader 11 (JG 11—11th Fighter Wing) where he was appointed Staffelkapitän of 10.

[26] On 17 May 1944, seven RAF North American P-51 Mustang fighters from the Second Tactical Air Force attacked the Aalborg Airfield in Denmark.

[27] On 1 June 1944, he was appointed Gruppenkommandeur (group commander) of I. Gruppe of JG 11 to replace Oberleutnant Hans-Heinrich Koenig who was killed in action on 24 May.

One week later, and two days after the Normandy landings Siegfried Simsch was shot down by a North American P-51 Mustang and killed on 8 June 1944 over Rennes, France.