had two speed settings which governed their range: either at , or at . Fire-control The main guns of the G3 battlecruisers could be controlled from any of the three director-control towers (DCT). The primary DCT was mounted at the top of the forward superstructure. Another was mounted on the roof of the conning tower in an armoured hood and the third was aft. Each main gun turret was provided with a coincidence rangefinder in an armoured housing on the turret roof. The secondary armament was primarily controlled by three DCTs. Two mounted on each side of the bridge and the third was aft. The anti-aircraft guns were controlled by a high-angle control system mounted on the very top of the forward superstructure. Each pom-pom mount had its own director and there was also a height-finder aft. Two torpedo rangefinders were located on the sides of the funnels. Armour A first for any British dreadnought was the use of the all or nothing protection scheme in the G3s. Medium-thickness armour had proven to be useless in stopping heavy-calibre shells during World War I so the vital areas of the ship were protected by the thickest possible armour and the rest of the ship was left unarmoured. Use of this system was pioneered by contemporary U.S. Navy battleship designs starting with the . However, this system of protection required that the armoured citadel should have enough reserve buoyancy to keep the ship stable even if the rest of the hull was riddled by gunfire. The waterline belt of the G3 had a maximum thickness of with the top of the armour angled 18° outwards. This angle increased the armor's relative thickness to horizontal, close-range fire, albeit at the cost of reducing its relative height which increased the chance of plunging shellfire going over or under it. It ran some , from the forward edge of 'A' barbette to the rear of the after 6-inch magazine. The belt had a height of , of which was below the designed waterline. Only the forward of the belt had the maximum thickness, it thinned to for the rest of its length. The lower edge of the belt abreast the magazines was continued down another by a thickness of high-tensile steel inclined at 36° to prevent a shell from reaching the magazines via a wave trough at high speed. The forward and rear ends of