This a/c was the first YRF-110 Spectre built, later designated YRF-4C. Originally being built as a USN F4H-1, it was converted on the assembly line to USAF specifications. After finishing its career as a YRF-4C test a/c, it was modified into the prototype F-4E, and was also used for advanced development testing including fly-by-wire flight testing. It is currently at the USAF Museum but appears to be in storage as of 2021.