Johan Didrik Schlömer Beichmann KBE (30 May 1886 – 10 February 1966) was a Norwegian military officer, journalist and businessman.
A resistance pioneer during the German occupation of Norway, he fled to London and eventually served as head commander of the Norwegian Army-in-exile.
He studied electrical engineering at the Technische Universität Darmstadt (1908–1908), and graduated from the Norwegian Military College in 1911.
From 1912 to 1917 he headed Infantry Regiment 16, and was also periodically assigned as topographer for the Norwegian Mapping and Cadastre Authority.
In 1941 he was in command of local so-called "fighting groups", which eventually developed to become part of the resistance organization Milorg.