From Joe Baugher: 

Douglas XA-26F Invader

The XA-26F was a prototype for a high-speed version of the Invader. A single A-26B-61-DL (44-34586) was modified as the XA-26F prototype. It was fitted with a pair of 2100 hp R-2800-83 engines initially driving three-bladed propellers but later fitted with four-bladed units with large spinners. In addition, a 1600 lb.s.t. General Electric J31 turbojet was installed in the rear fuselage, with the exhaust pipe in the tail and fed by an intake above the central portion of the fuselage in place of the usual dorsal turret and gunner position. The eight-gun nose and the six wing 0.50-inch machine guns were retained.

With all three engines running at full power, the aircraft achieved a maximum speed of 435 mph at 15,000 feet. However, this was deemed to be an insufficient performance improvement over the proposed A-26D to warrant any production.

Sources:

  1. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian Institution Press, 1989.
  2. McDonnell Douglas Aircraft Since 1920: Volume I, Rene J. Francillon, Naval Institute Press, 1988.
  3. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.