Piper sold 19,073 J-3 piston-single aircraft between 1938 and 1947. The majority of them were L-4s and other military variants. These served in World War II and were also utilized by the US and South Korean Air Force in the early 1950s. As a military aircraft, the L4 primarily flew on weaponry spotting, reconnaissance, and forward air control missions, and several variants were developed, including the L-4J. An impressive 1,680 L-4Js were produced, each powered by a 65hp Continental O-170-3 engine, and incorporating a controllable pitch propeller.