The Douglas F6D Missileer was a proposed carrier-based US Navy fleet defense fighter aircraft, designed by Douglas Aircraft Company in response to a 1959 US Navy requirement. It was designed to be able to loiter for extended periods at relatively long distance from the Navy's aircraft carriers, engaging hostile aircraft 100 mi (161 km) away with its powerful radar and long-range missiles. Since the enemy would be fired on long before they reached visual range, the aircraft had little dogfighting capability and was strictly subsonic. When doubts were expressed about the Missileer's ability to defend itself after firing its missiles, the value of the project was questioned, leading to its cancellation. Portions of the Missileer continued development in spite of the cancellation, eventually emerging on the ill-fated General Dynamics/Grumman F-111B and successful Grumman F-14 Tomcat years later.