about with a shell at a muzzle velocity of . No anti-aircraft (AA) armament was originally planned. In October 1916, the Naval Ministry specified that four 37-caliber guns of a new design were to be fitted, but they never entered service. The two older ships had three or four 50-caliber Pattern 1892 guns mounted on turret roofs. The 75 mm gun had maximum elevation of 50°. It fired a shell at a muzzle velocity of at a rate of fire of 12–15 rounds per minute. It had a maximum ceiling of less than . Volia used four of the newer 30-caliber 'Lender' AA guns, mounted on the fore and aft turrets. This had a maximum depression of 5° and a maximum elevation of 65°. It fired a shell at a muzzle velocity of . It had a rate of fire of 10–12 rounds per minute and had a maximum ceiling of . Four underwater torpedo tubes were also fitted, two on each broadside in a compartment immediately abaft the forward magazine. Imperatritsa Mariyas trials revealed problems with her magazine cooling systems where the heat generated by the ventilation system mostly negated the cooling effects of the refrigeration system. Her sisters shared this problem, which may have contributed to the magazine fire suffered by Imperatritsa Mariya that led to her loss in 1916. The two older ships mounted Zeiss rangefinders on each conning tower, but Volia was given four Barr and Stroud rangefinders, one for each turret. These would provide data for the central artillery post to calculate, using the standard Geisler mechanical computer, and then transmit to the guns for the gun crew to follow. Armor The full-scale armor trials with the hulk of the old pre-dreadnought battleship greatly affected the armor protection of the Imperatritsa Mariya-class ships. The Krupp cemented armor plates were sized to match the frames to provide support for their joints and they were locked together by a type of mortise and tenon joint to better distribute the shock of a shell's impact. The waterline belt had a maximum thickness of . It was continued forward and aft of the citadel by plates and thick. These reduced to and then to 75 millimeters just before the bow. Aft the belt thinned to 125 millimeters all the way to the stern. It had a total height of , of which was above the design waterline and below.