Red Queen.

About Red Queen

Red King and Red Queen were experimental revolver cannon anti-aircraft guns developed for the British Army during the 1950s. Red King was a two-barrel design from Oerlikon, Red Queen was a single-barrel water-cooled design. The project was cancelled with the introduction of the Bofors 40 mm/L70, which became the standard anti-aircraft gun for the Army until it was replaced by the Rapier missile in the 1970s.