Gun Control Tower
A Gun Control Tower (often abbreviated as "G.C.T.") on a British capital ship was a cylindrical or oval-shaped armoured structure located forward atop or behind the Conning Tower which housed rangefinders and instruments dedicated to gunnery control. They were first introduced into service in the Orion and Lion classes.
In earlier vessels such as Queen Mary, the G.C.T. often had an armoured rangefinder position. From the Queen Elizabeth class and later capital ships, it was surmounted by an Armoured Tower containing a secondary director for the main guns as well as a 15-foot rangefinder.
- The Director Firing Handbook. p. 41.