Red Queen was a twin-barrelled 42mm (1.6") anti-aircraft gun that was developed by Oerlikon to replace the 40mm bofors guns that the Army and RAF used for air defence. Red Queen was the outcome of various studies on how to increase AA gun rates of fire, one of which was called "Ratefixer".
Apart form the twin barrels, Red Queen was unique because it had a magazine about 10ft (3m) in diameter on the left hand side of the gun. The rounds were arranged within this drum in a spiral, with the base of the cases towards the periphery.
Red Queen was cancelled in favour of guided weapons such as Mauler andPT.428. both of which were cancelled in favour of Rapier.
A related medium anti-aircraft gun wasGreen Mace.
Anti-Aircraft Guns or Colour Codes