He joined the military service as a Fahnenjunker (Officer Cadet) in the 2nd Infantry Regiment (Infanterie-Regiment 2) on 1 April 1931.

Staffel (10th squadron) of Lehrgeschwader 1 (LG 1—1st Demonstration Wing) flying the Heinkel He 111 bomber.

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

[3] On 29 March 1941, Crüger and led his group in an attack against a British task force southwest of Crete.

The group claimed three hits on the aircraft carrier HMS Formidable earning him a reference on 30 March 1941 in the Wehrmachtbericht (armed forces report), an information bulletin issued by the headquarters of the Wehrmacht.

Flying the Junkers Ju 88 A-4 3Z+AA (Werknummer 8627—factory number) he failed to return from a combat mission against the British forces on Malta.