In 1940, Alexander Kartveli, vice president and technical director of the Republic Aircraft Corporation, drew up plans for a new escort fighter built around the proposed 2350-hp Wright R-2160 Tornado, an experimental 42-cylinder, six-row liquid-cooled radial engine driving contrarotating propellers. Designated Model AP-18 by the company, the aircraft was envisaged as a potential replacement for the P-47 Thunderbolt when that aircraft became obsolescent.
The Wright Tornado engine was one of the most odd engine products of the entire American aircraft industry during the Second World War. It was a oddity in that it was a LIQUID-cooled radial engine. The 42 cylinders were arranged in six radial banks. This configuration was chosen so that the Tornado engine would have an extremely small overall diameter, enabling aircraft designers to build fuselages with small cross section areas. However, the Tornado required the use of rather heavy and complicated systems of cooling radiators, which probably would have negated any aerodynamic advantage it might have otherwise had.
In the XP-69, the Tornado engine was to be located immediately ahead of the pilot, and was to drive a set of contrarotating propellers. This is in contradiction to some other reports, which had the engine located immediately behind the pilot, and driving the propellors via an extension shaft. The air intake was located underneath the fuselage, and the ducts, the intercooler, the supercharger, and the cooling system were located immediately behind the pilot's cockpit. The pressurized cockpit featured a large bubble canopy. A laminar flow wing was planned. Proposed armament was two 37-mm cannon and four 0.50-inch machine guns, all mounted in the wings situated so that they fired outside the radius of the propellers.
Estimated performance included a maximum speed of 450 mph at 35,000 feet, a service ceiling of 48,900 feet, and a climb to 35,000 feet in 20 minutes. Maximum range was to have been 1800 miles. Estimated weights were 15,595 pounds empty, 18,655 pounds gross, 26,164 pounds maximum. Dimensions were wingspan 51 feet 8 inches, length 51 feet 6 inches, height 17 feet, and wing area 505 square feet.
In July 1941, the USAAF ordered two prototypes of the AP-18 under the designation XP-69. A P-69 mockup was inspected in June of 1942. However, delays in the delivery of the Wright Tornado engine caused the XP-69 project to be cancelled on May 11, 1943 in favor of Republic's parallel XP-72 project which showed more promise. In the event, the Tornado engine project was itself cancelled before anything could be built.