Violet Friend was the Ministry of Supply rainbow code for an anti-ballistic missile (ABM) system developed in the United Kingdom. The project began in 1954 with study contracts for an early warning radar system, which was followed by the February 1955 release of Air Staff Target 1135 (AST.1135) calling for a system to counter intermediate range ballistic missiles (IRBMs) being fired at the UK from eastern Europe. AST.1135 required the system to be able to attack six targets at once and be ready for initial deployment in 1963.
After many changes, due both to technical progress and changes in the strategic mission, in 1958 an interim design emerged that used existing missiles and radars to lower development costs. The concept used AMES Type 85 radars in East Anglia for long-range early detection as soon as the missiles rose above the radar horizon. Initial tracking of the warheads would then be handed off to AN/FPS-16 radars in the UK and the Netherlands. As they approached the UK, track information from the FPS-16 would direct an AMES Type 86 fire control radar to begin illuminating each selected target.
The enemy warheads would be attacked by a nuclear-armed Bloodhound Mk. 3, with interceptions taking place between 30,000–40,000 ft (9,100–12,200 m). Due to the short flight times of the ballistic missiles and relatively slow speeds of the Bloodhound, the Bloodhound had to be launched within 30 seconds of the initial early warning. The Bloodhound would at first fly under direct radio control from the ground while the warhead was still too far to be illuminated, and would then do a "jerk" manoeuvre onto the target trajectory once the Type 86 picked it up.
The project took place during an extended debate about the nature of the defence, ongoing since 1947. By the late 1950s, the plan was to move the deterrent from the V bomber fleet to the silo-based Blue Streak IRBM. It was believed the Soviets would be able to directly attack these by about 1970, and an ABM would be needed to retain the deterrent. Protecting the silos required a new ABM with improved performance, but the cancellation of the Blue Streak in 1960 ended much of the system's raison d'être. Ongoing concerns about the size of the Soviet missile fleet and the use of radar decoys led to serious questions about any system's effectiveness. Development largely wound down in 1960, and was formally abandoned in 1965.