On the outbreak of the War the Nazi leadership sought to utilize Niedermayer's knowledge of Slavic culture to assist with the management of occupation of Poland, however, he used personal contacts amongst the Army general staff to agitate for a more active role in the war for himself. Nevertheless, he again rejected the High Command of the Army's request on 20 February 1941. Thus Niedermayer turned down on 25 May 1941 again personally to
Wilhelm Keitel (1882–1946), the chief of OKW. Admittedly, he had the opportunity to participate in some courses, but until 30 May 1942 Niedermayer stayed with the leadership of the
162nd Turkoman Division instructed. This was not a regular Division, but simply a bar, which was scheduled, in the hinterland of the
Army Group in the South of
Ukraine, from (Caucasian, Turkestani, Georgian, Armenian) POWs troops formed against the Soviet Union's advance in Ukraine. This task was transferred to him, because he was known in the previous years, due to many articles and memoirs as a connoisseur of the geography and peoples of the profiled regions. The division was first installed in Ukraine, where they and Niedermayer were responsible for the training of the so-called "
Ostlegionen", until February 1943, and from then to autumn of 1943 they were reinstalled in Neuhammer German Reich. There the Legion was reclassified as a
Division, but it was still made of Caucasian, Georgian and Turkotartari soldiers. As commander of this division in
Operational Zone of the Adriatic Littoral, he fought against
Slovene Partisans in the
Battle of Kočevje, rescuing the besieged garrison in
Kočevje. In March 1944, the
Ostlegionen relocated to
Italy, to try to halt the Allied advance there as a part of the
10th Army, the Division deployed in Italy on 9 June 1944 on an increasingly precarious front, however Niedermayer by this time was no longer its Commander, having been replaced on 21 May 1944 on the orders of Field Marshal
Albert Kesselring, who had few weeks before in a written personal assessment of Niedermayer reported: "His education is above average... It is, however, more of a scholastic nature than of use in a practical fighting command application. in decision-making he is hesitant, and his command leadership style is too slow in reaction." (Cited in: Seidler, Franz W.: Oskar Ritter von Niedermayer im Zweiten Weltkrieg, in: Wehrwissenschaftliche Rundschau 20 (1970), S. 203.) Niedermayer now became the commander of voluntary associations by the Supreme Commander of Weststaggered. The details of his work there are not known. However, in August 1944, he had come to a view which was disparaging of Hitler's Ostpolitik. Two officers of his staff reported this to the Nazi Authorities and Niedermayer was arrested and charged with advocating
defeatism against
Nazi Germany. He was
Court Martialed at
Torgau. Numerous friends and associates, including
Heinrich Himmler, provided character references during the hearing stating Niedermayer's merits and history of service to Germany, but he was jailed and not released from Torgau prison until end of the war. After the
capitulation of Germany on May 9, 1945, whilst attempting to return to his hometown of Regensburg, at
Carlsbad the
Red Army arrested him, and he was deported to the U.S.S.R, and a Moscow prison, where he contracted
tuberculosis. A Russian
court martial sentenced him to 25 years in prison, which he was sentenced to serve in the prison of
Vladimir (German: Wladimir), where he died on 25 September 1948 in the prison's hospital. == Works ==