Few aircraft were as important for the efficient conduct of war operations in Vietnam as the small, unarmed Cessna O-1B, previously known as the L-19. Spearhead of the FAC (Forward Air Control), it formed part of the US Army organization until 1965, when all fixed-wing observation aircraft were turned over to the USAF. Flying at low level and reduced speed, their duty was to discover objectives, for the most part concealed in the jungle, such as groups of guerillas, convoys traveling along the Ho Chi Minh Trail, or enemy units lying in ambush for unsuspecting government troops. Having spotted the enemy, they would immediately radio the DASC (Direct Air Support Center) which, as a rule, would be able to get attack aircraft to the spot within half an hour. The latter were again guided by the Bird Dog pilots who, in addition to pinpointing the objective with smoke or magnesium flares, would check the effectiveness of the strikes, if necessary correcting the aim. However, the O-1s were an easy target for the enemy, who could often hit them with ordinary rifle fire, without recourse to heavy anti-aircraft fire. Many Bird Dog pilots lost their lives while carrying out their duty; they were usually officers with years of experience, veterans of many battles. Among the finest fighters, they succeeded in converting their little unarmed planes into formidable offensive weapons.