The final source of supply was Allied air drops, which was the only way to obtain more exotic, highly useful equipment such as plastic explosives and antitank weapons such as the British PIAT. During the war, 485 air-drop missions from the West (about half of them flown by Polish airmen) delivered some 600 tons of supplies for the Polish resistance. Besides equipment, the planes also parachuted in highly qualified instructors (Cichociemni), 316 of whom were inserted into Poland during the war.