 The Royal Sovereigns ' armour scheme was similar to that of the Trafalgars , as the waterline belt of compound armour only protected the area between the barbettes . The 14 – 18 @-@ inch ( 356 – 457 mm ) belt and transverse bulkheads 14 – 16 inches ( 356 – 406 mm ) thick closed off the ends of the belt . Above the belt was a strake of 4 @-@ inch ( 102 mm ) nickel @-@ steel armour closed off by 3 @-@ inch ( 76 mm ) transverse bulkheads . The barbettes were protected by compound armour , ranging in thickness from 11 to 17 inches ( 279 to 432 mm ) and the casemates for the 6 @-@ inch guns had a thickness equal to their diameter . The thicknesses of the armour deck ranged from 2 @.@ 5 to 3 inches ( 64 to 76 mm ) . The walls of the forward conning tower were 12 – 14 inches ( 305 – 356 mm ) thick and the aft conning tower was protected by 3 @-@ inch plates . 
