The outbreak of hostilities in Europe in 1939, along with the growing realization that the United States might soon be drawn into World War II, resulted in the formation of the Civilian Pilot Training Program (CPTP). The Piper J-3 Cub became the primary trainer aircraft of the CPTP and played an integral role in its success, achieving legendary status. About 75% of all new pilots in the CPTP (from a total of 435,165 graduates) were trained in Cubs. By war's end, 80% of all United States military pilots had received their initial flight training in Piper Cubs.