He was initially assigned to the Infantry, then in 1912 he was transferred to Signal Corps (Nachrichten Telegrafen Bataillon) in Frankfurt (Oder).
Selchow at the time fervently wished to resign by was persuaded to stay by von Bülow, who until 1938 was Secretary of the Ministry of Foreign Affairs, when he died.
During World War II, he had no exact knowledge of the messages passed between different parties, and took no part in any matters pertaining to diplomacy.
In 1950, the Federal Foreign Office tasked Selchow along with Erich Hüttenhain, Heinz Kunze (1890-1970) and Rudolf Schauffler to form a cryptographic service under the direction of Adolf Paschke that was called Section 114.
[5] The service was to act as a cypher bureau for the Central office of Encryption (ZfCh) (German: Zentralstelle für das Chiffrierwesen) that had been previously created in 1947 and was located at Camp King.