Serving in the infantry in the final battles of World War I, Foertsch earned the Iron Cross second class before the end of hostilities.

He again served in many senior positions, including an assignment to the Supreme Headquarters Allied Powers Europe (SHAPE) of NATO in Paris.

Shortly before the end of World War I he participated in the battles of the Schelde at the Wotan- und Hermann positions northeast of Lille and was awarded the Iron Cross 2nd class.

[2][3] With his brother, Foertsch joined the Freikorps "Feldmarschall Hindenburg" after the war and was accepted by the Reichswehr at the end of 1920, serving as a Fähnrich (ensign) in the 17.

The Weimar Republic largely obeyed the Versailles restrictions, but with Adolf Hitler's rise to power the remilitarisation began.

Armeekorps (3rd Army Corps) on 10 November 1938, a position he held at the outbreak of World War II.

On 1 June 1942 he was promoted to Oberst im Generalstab and at the same time appointed first officer of the general staff of the 18th Army.

Foertsch earned the German Cross in Gold on 10 May 1943 for his support in the heavy fighting in the northern sector of the eastern front.

He was appointed chief of the general staff of the 18th Army on 1 December 1943 and promoted to Generalmajor on 1 June 1944.

He was sentenced to 25 years' imprisonment for war crime charges against the destruction of cities and art on 29 June 1950.

He was then posted to the Supreme Headquarters Allied Powers Europe (SHAPE) of NATO in Paris as deputy chief of the fundamental planning office.

He was also in command during the political Spiegel scandal, which led to the resignation of Federal Minister of Defence Franz Josef Strauß.

Der Spiegel, a widely read German periodical, had published the article "Bedingt abwehrbereit" ("Conditionally prepared for defense") about a NATO maneuver called Fallex 62, Fall Exercise 1962, in which the NATO forces were to demonstrate their preparedness to resist possible attack by the Soviet Union and/or other Eastern Bloc forces.