A report on Blue Envoy, Seaslug (missile) and Rainbow Code

Seaslug Mk. II missile
Seaslug on display at Wickenby Aerodrome, Lincolnshire, UK
Test firing from the trials ship HMS Girdle Ness (A387), circa 1961.
The Seaslug launcher mounted on the quarterdeck of HMS Glamorgan, circa 1972
The firing of the first Seaslug test missile from HMS Girdle Ness (A387). This version is based on the RAE's early GPV, and retains the rear-mounted boosters before they moved forward on the "long round".
Map with Seaslug operators in blue

Blue Envoy (a Rainbow Code name) was a British project to develop a ramjet-powered surface-to-air missile.

- Blue Envoy

It was planned that Seaslug's medium-range role was to be supplanted by a very long-range missile known as Blue Envoy, but this was passed over in favour of a new medium-range system, Sea Dart.

- Seaslug (missile)

Blue Envoy – surface-to-air missile to OR.1140, replaced Green Sparker as "Stage 2" SAM

- Rainbow Code

Blue Shield – see Armstrong Whitworth Sea Slug

- Rainbow Code

They started the New Guided Missile Program, or NIGS for short, to replace the existing Seaslug missile on the County-class destroyers with a missile of much higher performance and a fire control system and radar that could track multiple targets, similar to the modern Aegis Combat System.

- Blue Envoy

The Seaslug Mark 2 was based on the aborted Blue Slug programme to develop an anti-ship missile using the Seaslug missile and guidance system.

- Seaslug (missile)
Seaslug Mk. II missile

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Thunderbird II at Imperial War Museum Duxford

Thunderbird (missile)

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British surface-to-air missile produced for the British Army.

British surface-to-air missile produced for the British Army.

Thunderbird II at Imperial War Museum Duxford
Thunderbird II at Imperial War Museum Duxford
A Thunderbird I missile minus finned-boosters, a museum exhibit at the Midland Air Museum, England.
Thunderbird missile (front)
Colourful display of Thunderbird II airframe in Anti-Aircraft Museum, Tuusula, Finland. Note the changes to the main fins.
Missile rear end connector details. The Artillery Museum of Finland, Hämeenlinna.
Thunderbird at RAF Museum Cosford

From their work the LOPGAP experimental design emerged, short for "Liquid Oxygen and Petrol Guided Anti-aircraft Projectile".

As a new project, it was assigned a name under the newly-introduced MoS rainbow code, "Red Heathen".

The original Red Heathen concept for a much longer-ranged weapon became "Green Sparkler" and then "Blue Envoy", and relegated to Stage 2 deployment in the 1960s along with newer radars and interceptor aircraft.