He entered the German Imperial Army as a Fähnrich in the 86th Regiment of Fusiliers on 29 March 1916, and was commissioned a Leutnant a week prior to his eighteenth birthday.

In the following August he began service with Luftstreitkräfte as an observer, and continued this duty to the end of World War I.

Deichmann was released as a POW on 22 December 1947, having already completed his first writings for the Operational History (German) Section of the Historical Division of the United States Army.

From 1952 to 1958, he was the control officer and therefore head of the "German Air Force Monograph Project" of the USAF Historical Division in Karlsruhe.

He was then appointed head of a historical study group (Studiengruppe) at the Führungsakademie der Bundeswehr (FüAkBw), where he also gave numerous lectures.