From 1909 to 1933 he held various positions in the Norwegian General Staff. In addition he served as a captain and commanded Company 4 of the Norwegian Royal Guards in 1926–1929, chief of the Commanding General's staff of adjutants in 1933-1934 and as a teacher at the Norwegian Defence Staff College in 1928–1934. He also edited the military journal "Norsk Militært Tidsskrift". During his time at the General Staff Fleischer warned of the possibility of a surprise attack on central areas of Norway. He also stated that the best way of confronting such an attack was a combination of defending coastal outposts while the main forces mobilised in rear areas in the interior of the country.