one turret was modified to control the entire main armament later in the war. A director for the guns was added on each side in 1916–17. A high-angle rangefinder was added in 1918 to the spotting top. Armour So much weight had been devoted to Agincourts armament that little remained for her armour. Her waterline belt was just thick, compared with twelve inches or more found in other British dreadnoughts. It ran some , from the forward edge of "Monday" barbette to the middle of "Friday" barbette. Forward of this the belt thinned to six inches for about before further reducing to all the way to the bow. Aft of the midships section the belt reduced to six inches for about and then thinned to four inches (102 mm); it did not reach the stern, but terminated at the rear bulkhead. The upper belt extended from the main to the upper deck and was six inches thick. It ran from "Monday" barbette to "Thursday" barbette. The armour bulkheads at each end of the ship angled inwards from the ends of the midships armoured belts to the end barbettes and were three inches thick. Four of Agincourts decks were armoured with thicknesses varying from . The armour of the barbettes constituted a major weakness in Agincourts protection. They were 9 inches thick above the upper deck level, but decreased to 3 inches between the upper and main decks and had no armour at all below the main deck except for "Sunday" barbette (which had 3 inches), and "Thursday" and "Saturday" barbettes (which had 2 inches). The turret armour was 12 inches thick on the face, on the side and in the rear. The turret roofs were 3 inches thick at the front and 2 inches at the rear. The casemates for the secondary armament were protected by 6 inches of armour and were defended from raking fire by 6-inch-thick bulkheads. The main conning tower was protected by 12 inches of armour on its sides and it had a 4-inch roof. The aft conning tower (sometimes called the torpedo control tower) had 9-inch sides and a 3-inch roof. The communications tube down from each position was 6 inches thick above the upper deck and 2 inches thick below it. Each magazine was protected by two armour plates on each side as torpedo bulkheads, the first one an inch thick and the second