Martin XO-4
The Martin XO-4 was a proposed observation aircraft designed by the Glenn L. Martin Company. It was designed to compete with the Curtiss XO-1, Douglas XO-2, and Dayton-Wright XO-3, and was to be powered by a Wright [T-3 Tornado] or a Liberty V-1650. Although it failed to receive a contract from the United States Navy, a single prototype was ordered by the United States [Army Air Service], but this contract was canceled before the prototype could be built.