The Rainbow Codes were a series of code names used to disguise the nature of various British military research projects. They were mainly used from after the Second World War until 1958, when they were replaced by an alphanumeric code system.
During WWII, British intelligence was able to glean details of new German technologies simply by considering their code names. For instance, when they began hearing of a new system known as Wotan, Reginald Victor Jones asked around and found that Wotan was a one-eyed god. Based on this, he guessed it was a radio navigation system using a single radio beam. This proved correct, and the Royal Air Force was able to quickly render it useless through jamming.
Looking to avoid making this sort of mistake, Ministry of Supply (MoS) initiated a system that would be entirely random, while still being easy to remember. Each rainbow code name was constructed from a randomly selected colour, plus an (often appropriate) noun taken from a list, for example:
"Green" + "Mace" = Green Mace, an anti-aircraft (AA) gun.
While most colour and noun combinations were meaningless, some were real names, although quite unrelated to the project they designated. For example, "Black Maria" is also a name for a police van and the "Red Duster" is a name for the Red Ensign, the flag flown by British merchant ships. Some code names were not assigned through the official system, but created to sound like it. An example is the Blue Yeoman radar, an unofficial name created by combining the names of two other projects, Blue Riband and Orange Yeoman.
The names were mostly dropped with the end of the Ministry in 1959. Its functions were transferred to the War Office, the Air Ministry that handled military aviation, and the newly created Ministry of Aviation in charge of civil aviation. After the reorganization, projects were mostly named with randomly selected codes comprising two letters and three digits, e.g. BL755, WE.177. However, rainbow codes continue to be used with some modern systems; current examples include the Blue Vixen radar
and the Orange Reaper Electronic Support Measures system.
Pink Hawk - early name for Fairey Fireflash missile. As this was a "reduced" version of the Red Hawk, it is a rare example of Rainbow Codes having some implied meaning, rather than their usual purely deliberately meaningless choice.
Yellow Temple - nuclear-armed SAGW development of Red Shoes
Yellow Tiger - Target illuminating radar used with the Thunderbird missile.
Yellow Veil - ALQ-167 pod for Royal Navy Lynx.
Several British military related terms have a similar format to Rainbow Codes, but are not since they do not refer to classified research projects, and some names have been used unofficially. These include:
Black Banana - unofficial nickname for the Blackburn Buccaneer, originally named the Blackburn ANA (Blackburn Advanced Naval Aircraft).
Blue Circle - sardonic name for concrete ballast for Buccaneer while awaiting Blue Parrot radar. Also used for Sea Harrier ballast in place of Blue Fox radar, and Tornado F.2 ballast. From the Blue Circle cement company.
Green Meat - a 'spoof' SAM programme reported in the 1976 RAF Yearbook
Green Parrot - unconfirmed low yield nuclear weapon mentioned in a 1981 New Statesman article by Duncan Campbell who later claimed that it was "probably" a copy of the B57 nuclear bomb. The WE.177 has incorrectly been referred to as the Green Parrot by some authors. However Green Parrot was a NATO codename for the Soviet PFM-1 anti-infantry mine. Green Parrot was also the term for an admiral's barge, traditionally with a green-painted hull.