War Department tradition and policy mandated the segregation of African-Americans into separate military units staffed by white officers, as had been done previously with the 9th Cavalry, 10th Cavalry, 24th Infantry Regiment and 25th Infantry Regiment. When the appropriation of funds for aviation training created opportunities for pilot cadets, their numbers diminished the rosters of these older units. In 1941, the War Department and the Army Air Corps, under pressure — three months before its transformation into the USAAF — constituted the first all-black flying unit, the 99th Pursuit Squadron.