III derated the motor to limit acceleration when launched from new supersonic interceptors in order to avoid overheating due to aerodynamic friction.

[2] F.155 was canceled in the aftermath of the release of the 1957 Defence White Paper, as Duncan Sandys noted that it would not be in service before new Soviet ballistic missiles had rendered the need for crewed interceptors moot.

This argument was successfully countered by the Air Ministry, which pointed out that the Tupolev Tu-22 "Blinder" would be in service in 1962 resulting in a several-year gap where the RAF had no effective response.

More importantly, they no longer required active cooling, which in Firestreak had been accomplished with an aircraft-mounted system using ammonia, presenting a ground-handling safety issue.

Removing the ammonia bottles and all of the plumbing for the cooling systems freed up room in the electronics section and the aircraft-mounted weapon pack.

For Red Top, the all-aspect lead telluride (PbTe) seeker developed for Blue Vesta was replaced by a much less expensive indium antimonide (InSb) system known as "Violet Banner".

In contrast to Blue Vesta, which retained most of the original Firestreak physical layout, Red Top significantly rationalised the design.

[3] In Red Top, the smaller electronics package allowed the warhead to be moved forward, leaving room for the control actuators to be mounted directly on the fins and thus removing the need for the pushrods.

Moving the actuators to the rear, along with the air bottle that powered them, still took up much less room than the warhead, allowing the rocket motor to be made larger by extending it rearward.

This move also left room at the rear of the fuselage for one of the two rows of the IR proximity fuse, which were formerly positioned just in front of the mid-mounted wings.

The Air Staff argued this point, ultimately convincing him that Red Top's head-on attack profile against new Soviet supersonic bombers known to be in development was an urgent requirement.

[5] At a February 1958 meeting of the Controller of Guided Weapons and Electronics, the group earmarked Red Top for both Lightning and the Fleet Air Arm's de Havilland Sea Vixen.

There was also some discussion of mounting four Red Top on Blackburn Buccaneer, likely the B.112 version that had been proposed to replace Sea Vixen for long-duration combat air patrol.

The concept fit the aircraft with a more powerful engine, added the AIRPASS radar from the Lightning, and carried a pair of Red Top missiles.

[9] Red Top testing began using the new fuselage layout with the original Firestreak faceted nosecone and leftover Magpie III motors from the Blue Vesta program.

[9] When plans began to introduce the McDonnell Douglas Phantom in UK service, the issue was raised about the inclusion of Red Top on that platform.

It also had roughly double the maximum engagement angle, when radar cued, which gave the interceptor improved tactical freedom on their choice of approach.