Fischer's career as an officer began in German West Africa, present-day Namibia, to which he was sent in 1904 to take part in the brutal subjugation of the Herero people. He was later stationed at Fort Namutoni in the northern part of the colony where he became the first Game Warden of the Etosha National Park. He remained in Africa until 1913 when he returned to Germany, and the following year he published the book Menschen und Tiere in Deutsch-Südwest. At the beginning of the First World War, he was placed in the Ottoman Empire, where he participated in the Sinai expedition. He returned to Germany in 1917 and came during the last years of the war to work with the exchange of prisoners of war. In November 1918, Fischer was contacted by acquaintances of Erich Ludendorff who needed help to bring the General-quartiermeister out of the country. Fischer escorted Ludendorff to Copenhagen and then on to Sweden. After the War, he settled in Copenhagen.