Lots of confusion here. The YF5D-1 Skylancer was a follow-on all-weather development to the Douglas F4D-1 (F-6) Skyray that began life as the XF4D-2N. As engineering progressed, the designation was changed to XF5D in recognition of the radical airframe and engine revisions. As for the F4D-1, it was redesignated the F-6 in 1962 when the U.S. Navy simplified and combined its aircraft designations with the USAF. The Skyshark was a third Douglas aircraft -- the A2D turboprop replacement for the AD (A-1) Skyraider.
The Navy rejected the F5D-1 in favor of the Chance-Vought (LTV) F8U (F-8) Crusader. Two prototypes and two service test models were constructed, and one of the prototypes and the final service test model were tranferred to NASA. The latter, flown by Neil Armstrong as part of the Dyna-Soar, is displayed outside the Neil Armstrong Museum in Wapakoneta, OH. 12/18/2004 @ 21:38 [ref: 8897]