Out of more than 40,000 applicants, 22,689 were accepted and 17,540 completed ground school training. Approximately 15,000 advanced to primary (preliminary) flying training, a six-to-eight week course conducted by both military and civilian flying instructors, using variants of the Curtiss Jenny as the primary trainer. Primary flying training school usually produced a candidate for commissioning in 15 to 25 hours of flight. At the assurance of the French that they could be rapidly trained in all phases, 1,700 cadets who had graduated from ground school were sent to Europe to undertake the entire flying portion of their training in Great Britain, France, and Italy. In December 1917, after receiving 1,400 of the cadets, the French requested that further movement of cadets be halted because of training backlogs of as much as six months, and no further student pilots were sent to France until they had completed their primary training and been commissioned. During the backlog, more than 1,000 cadets were used as cooks, guards, laborers and other menial jobs, while paid at cadet salary (in the grade and rank of private first class), for which they became derisively known as the "Million-Dollar Guard". The backlog was finally cleared by opening an Air Service primary school at Tours and devoting part of the advanced school at Issoudun to preliminary training for a period of time.