The American Douglas F4D Skyray (later redesignated F-6 Skyray) was a carrier-based fighter built by the Douglas Aircraft Company. Although it was in service for a relatively short time and never entered combat, it was notable for being the first carrier-launched aircraft to hold the world's absolute speed record and was the first United States Navy and United States Marine Corps fighter capable of exceeding Mach 1 in level flight.
The Skyray was designed to meet a Navy requirement issued in 1947 for a fighter aircraft capable of intercepting and destroying an enemy aircraft at an altitude of 50,000 ft (15,240 m) within five minutes of the alarm being sounded. The Navy also wanted an aircraft which followed the designs and research of the German aerodynamicist Alexander Lippisch who moved to the U.S. after World War II.
The F5D Skylancer was a cancelled development of the F4D Skyray.
The F4D Skyray was a wide delta wing design with long, sharply swept, rounded wings. The design was named after the Manta ray fish which it resembled.  The thick wing roots contained the air intakes feeding a single turbojet engine. Fuel was contained both in the wings and the deep fuselage. Leading-edge slats were fitted for increased lift during takeoff and landing, while the trailing edges were mostly elevon control surfaces. Additional pitch trimmers were fitted inboard near the jet exhaust, and were locked upward on takeoff and landing.
The Westinghouse J40 turbojet was the intended power plant, but Douglas fortunately took a conservative view and designed in contingency options for other power plants. The J40 proved troublesome and was eventually cancelled, and the Skyray was fitted instead with the Pratt & Whitney J57, a more powerful but larger engine.
Production aircraft were not delivered until early 1956, while the U.S. Marine Corps received their first in 1957. In total, 419 F4D-1 (later designated F-6 in the unified designation system) aircraft were produced.
Its unique and notable looks also played a part in making the Skyray one of the best-remembered early jet fighters. Affectionately known as the "Ford" (after the "Four" and "D" of its designation),  this aircraft had a spectacular rate and angle of climb and set a new time to altitude record. It saw the Skyray fly from a standing start to 49,221 ft (15,000 m) in 2 minutes and 36 seconds, all while flying at a 70 degree pitch angle. 
See main article: F5D Skylancer. A derived successor, the F5D Skylancer, was designed and prototypes were built and flown, but the project was cancelled as being too similar in mission parameters to the Vought F8U Crusader and also to reduce dependence upon Douglas Aircraft, which was also producing several other aircraft for the U.S. Navy. 
In April 1956, VC-3 was the first squadron operational with the F4D-1. This unit was later redesignated VFAW-3 and assigned to NORAD, as the only U.S. Navy squadron. VFAW-3 was permanently based at NAS North Island, San Diego. The US Marine Corps also flew the Skyray. When the Skyray was redesignated F-6A in September 1962, only VFAW-3, VMF-114, VMF-513 and VMF(AW)-542 flew the type together with the reserve squadrons VMF-215, VF-881 and VF-882. The last operational squadron was VMF(AW)-542 which used the Skyray until February 1964.
The Skyray was designed exclusively for the high-altitude interception role and was unsuited to the multi-mission capabilities soon in demand, so it had a short life in Navy and Marine Corps service, the last aircraft being withdrawn from service in 1964. Four aircraft were used by NACA (soon to be NASA) until 1969.
Under the new 1962 United States Tri-Service aircraft designation system, the F4D-1 was redesignated the F-6A. . The F4D (old designation) should not be confused with the F-4D (new designation) - the latter being the "D" variant of the McDonnell F-4 Phantom II.