On Mark Engineering was an American aircraft remanufacturing company established in 1954 at Van Nuys Airport in California. Its most significant products were rebuilding military surplus A-26 Invaders into executive transports—the Marketeer with an unpressurized fuselage and the Marksman with fuselage pressurization. On Mark converted 41 Douglas B-26s into one YB-26K and 40 B-26K Counter-Invaders (later redesignated A-26A) for counterinsurgency missions with the US Air Force.