Looking for an improved weapon for the Operational Requirement F.155 interceptors, in 1955 the Air Ministry issued OR.1131 for an all-aspect design capability against enemy aircraft traveling at Mach 2. De Havilland responded with Blue Jay Mk.4, which was later given its own rainbow code, Blue Vesta. This adopted the PbTe seeker of Mk.2, further improved by cooling it to improve its sensitivity in what became known as the "Violet Banner" seeker. The motor was further upgraded to the new Magpie III. To handle the aerodynamic heating issues, the fins were made of steel rather than aluminum, and featured cut-away sections to keep the rear portions of the surfaces out of the Mach cones, a feature they referred to as "mach tips". Work on Mk.4 was curtailed after 1956 as the RAE decided that the closing speeds of two Mach 2+ aircraft would be so rapid that the missile would have no chance to be launched while still within the range of its seeker.