Hosenfeld was drafted into the "Wehrmacht" in August 1939 and was stationed in Poland from mid-September 1939 until his capture by the Soviet Army on 17 January 1945. His first destination in Poland was Pabianice, where he was involved in the building and running of a POW camp. Next, he was stationed in Węgrów in December 1939, where he remained until his battalion was moved another 30 km away to Jadów at the end of May 1940. He was finally transferred to Warsaw in July 1940, where he spent the rest of the war, for the most part attached to "Wach-Bataillon" (guard battalion) 660, part of the "Wach-Regiment Warschau" (Warsaw Guard Regiment) in which he served as a staff officer and as the battalion sports officer. He was responsible for sport events at the Army Stadium in Warsaw.