A co-pilot was trained as a pilot and acted as support and backup for the main pilot of an aircraft. Having two pilots on a plane made made things easier while the aircraft was flying in formation or in combat and also allowed the pilots to rotate duties. Flying formation for eight to ten hours was strenuous work. This way, the pilot and co-pilot could swap duties, so that neither one wore himself out.
On occasion, co-pilots received training in other specialties, usually either navigation or bombardier training. This ensured that there was a backup crew member trained in these areas, in case one of the crew members responsible for these duties were unable to fulfill them during the mission.