In June 1939, the U.S. Navy placed a contract with the Steel Products Engineering Co. (SPECO) of Springfield, Ohio for one XB-4070-2 barrel engine, a concept also tried elsewhere, but never fully successful. In a barrel engine, the cylinders are parallel to the engine driveshaft and arranged radially around it; therefore producing a small frontal area. This version incorporated 9 cylinders having 18 opposed pistons, with the pistons rotating slowly to insure uniform heating and avoid thermal distortion. A swashplate (an inclined disc) located on the driveshaft in the center of the engine converted piston thrust to torque. This arrangement is inherently very compact and light in weight. However, the bearing problems involved in the swashplate mechanism were difficult to solve and did not result in a good high-output engine.
