rooms. The belt had a height of , of which was below the designed waterline. 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 ends of the belt terminated in transverse bulkheads. The armoured deck matched the length of the waterline belt and sloped down to meet the upper edge of the belt. It extended forward over the torpedo compartment which had a separate transverse bulkhead protecting it that was thick. The steering gear was protected by a deck and bulkhead thick. The turret faces were thick while their sides were probably in thickness, and the roof was 8 inches thick. The armour of the barbettes and the conning tower was 15 inches thick and the conning tower's communications tube to the upper deck was 8 inches thick. The fire-control director atop the conning tower was protected by an armoured hood 4 to 6 inches thick. The anti-torpedo bulges of the N3 were internal to the hull and were intended to withstand the explosion of a torpedo warhead. They consisted of an outer air space, an inner buoyancy space and the thick torpedo bulkhead. The bulkhead was situated about inboard from the side of the ship. Postwar tests done on a replica of this system showed that filling the buoyancy space with water rather than the sealed steel crushing tubes as used in was just as effective and weighed less. Cancellation The four N3 battleships were never ordered because the Washington Naval Treaty, an arms limitation treaty under negotiation at the time, forbade construction of any ship larger than 35,000 tons. Many of the aspects of their design ultimately were incorporated into the two s, and they are often described as being a cut-down N3. Indeed, the Nelsons received the design designation 'O3', marking them as next in the design sequence, although they used the guns intended for the G3 battlecruisers for cost reasons and to comply with the Treaty's 16-inch limitation on main armament. Though far from receiving names, the four vessels of the N3 design have since been associated, albeit speculatively, with the names of the four patron saints of Scotland, England, Ireland and Wales, those being HMS St. Andrew, HMS St. George, HMS St. Patrick and HMS St.