A prone pilot lies on their stomach rather than seated in a normal upright or reclining position.
During World War II it was suggested that a pilot in the prone position might be more effective in some kinds of high-speed aircraft, because it would permit the pilot to withstand a greater g-force in the upward and downward direction with respect to the plane.
Many speculative designs of the late-war and early postwar periods featured this arrangement, and several prototypes were built or converted to test the idea.
However testing revealed difficulties in maintaining a head-up attitude to see forward and in operating some controls.
Many hang gliders since the 1960s have allowed the pilot to lie prone in flight.