CO-1 to CO-8
Grover Loening had proposed to the Air Service on September 23, 1923, an amphibian aircraft that would use the same engine and layout as the DH-4B and have superior performance. Realizing the usefulness of such a type, especially to the three overseas observation squadrons in the “islands” and the Canal Zone, the Army ordered a prototype as the XCOA-l.
The prototype was ready on June 9, 1924, and although the first day’s trials ended with a wreck, ten COA-l amphibians were ordered in July. The first was flight delivered January 17, 1925, and immediately lived up to its promise. The wheels folded up by hand crank into the fuselage above the metal-covered hull, an inverted Liberty turned a four-bladed propeller, and while the wing had the DH-4 plan form, the Loening had an improved airfoil section, metal ribs and steel N struts. A Scarff ring around the observer’s cockpit could accommodate a Lewis gun for defense, and a fixed M1921 Browning was on the engine cowl.
Four COA-1s were transferred to the Navy and redesignated OL-2s for the 1925 McMillian Arctic Expedition. Army contracts for 15 OA-lA, 9 OA-lB, and 10 OA-lC amphibians followed. Similar to the OA-l, but for a three-bladed metal propeller, and new vertical tail, they were delivered from October 1926 to February 1928 from the Manhattan factory, and rapidly became famous for their usefulness in exploration, mapping and patrol of the overseas departments. The Army’s Pan-American Goodwill Flight begun from Texas on December 21, 1926, by five OA-1As, attracted international attention.
The XO-10 was a new Loening version, which was also known as the XOA-2. Powered by an experimental Wright Tornado inverted, air-cooled engine with a two-bladed propeller, it had a single main wheel retracting into the hull’s centerline. The XO-10 was flight delivered July 3, 1929, after eight more had been ordered as the OA-2. Performance tests were not completed until November and showed marked degradation of climb at high altitude.
The eight OA-2s were built at Bristol, Pennsylvania, by Keystone, who had bought Loening’s amphibian company, and delivered with the regular retractable twin-wheel gear from June to September 1930. The Tornado engine’s output was so poor that it took more than 59 minutes to climb to 10,000 feet, and this engine was never again used in an Army plane. While Keystone then offered an O-37 design as a counterpart of the Navy’s Wasp-powered OL-9, none were actually built.
Although the Army continued buying amphibians with OA designations, they were no longer combat planes with gun mounts, but were ordinary commercial types used for transport and utility service until World War II.