CFTC also operated aircrew schools for Navigators, Bombardiers and flexible aerial gunners. During World War II, Barksdale trained pilots, navigators, and bombardiers. Work began in earnest on a variant specifically for training military pilots, bombardiers, and navigators. Bombardiers and navigators attended either before or after they attended their training school. Of that total, 82,252 were classified as pilots, 21,842 as bombardiers and 14,230 as navigators. In World War II, over 90% of USAAF bombardiers and navigators trained in these aircraft. Chiang Kai-shek pilots and bombardiers received training from Kirtland Field instructors. The 51st class to complete the bombardier training course included 143 bombardiers. These soldiers included pre-aviation cadets, radio operators, aviation technicians, bombardiers, and aviation mechanics. Thayer testified that he never ordered the bombardiers, the Second Artillery, to police the barracks. These all used radio command-guidance from the bombardiers of the warplanes that launched them. Two belt tracks were common on early model Bombardiers and muskeg machines. Bombardiers released torpedoes at a breakwater some away. Liberator bombardiers began, and in September, a RADAR training school for bombardiers was established. The already delivered sets were moved back to Bombardiers Berlin plant for modifications.