In August 1956, the Fleet Air Arm took over development of the Blue Jay line with Blue Jay Mk.5, replacing the IR seeker with a semi-active radar homing (SARH) system intended to be used with the De Havilland Sea Vixen's AI.18 radar with a special continual wave illuminator mode. This was otherwise identical to Mk.4, differing only by replacing its seeker section with a longer ogive nose cone holding the radar receiver antenna. Problems fitting the illuminator antenna to the Sea Vixen ended work on this project. In November 1957 it was briefly restarted under the name Blue Dolphin as other radar-guided developments ended, but this was never deployed.