The primary aircraft used by the AEF at the front (the "Zone of Advance") were the SPAD XIII (877), Nieuport 28 (181), and SPAD VII (103) as pursuit aircraft, the DeHaviland DH-4B (696) and Breguet 14 (87) for daylight bombing, and the DH-4 and Salmson 2 A.2 (557) for observation and photo reconnaissance. The SE-5 operated as the main trainer for the Air Service. Balloon companies operated the French-designed Goodyear Type R, a winch-tethered, hydrogen-filled, captive "Caquot" observation balloon of 32,200 cubic-foot (912 cubic meters) capacity, deploying one balloon per company.