The Borodino-class battlecruisers () were a group of four battlecruisers ordered by the Imperial Russian Navy before World War I. Also referred to as the Izmail class, they were laid down in late 1912 at Saint Petersburg for service with the Baltic Fleet. Construction of the ships was delayed by a lack of capacity among domestic factories and the need to order some components from abroad. The start of World War I slowed their construction still further, as the imported components were often not delivered and domestic production was diverted into areas more immediately useful for the war effort.
Three of the four ships were launched in 1915 and the fourth in 1916. Work on the gun turrets lagged, and it became evident that Russian industry would not be able to complete the ships during the war. The Russian Revolution of 1917 halted all work on the ships, which was never resumed. Although some consideration was given to finishing the hulls that were nearest to completion, the three furthest from completion were sold for scrap by the Soviet Union during the early 1920s. In 1925, the Soviet Navy proposed to convert Izmail, the ship closest to completion, to an aircraft carrier, but the plan was cancelled after political manoeuvring by the Red Army cut funding and she was eventually scrapped in 1931.
Design and development After the end of the Russo-Japanese War of 1905, the Russian Naval General Staff decided that it needed a squadron of fast armoured cruisersMcLaughlin, p. 244 that could use their speed to engage the leader of an enemy's battle line, as Admiral Tōgō had done against the Russian fleet during the Battle of Tsushima. The Naval General Staff initially called for a ship with high speed (), guns, and limited protection (a waterline belt of ). The Tsar, head of the Russian government, approved construction of four such ships on 5 May 1911, but the State Duma session ended before the proposal could be voted on. Preliminary bids for the ships were solicited from private builders, but the bids proved to be very high, leading to a reconsideration of the requirements. The Naval General Staff issued a new specification on 1 July 1911 for a ship with a speed of only and with armour increased to . The armament was increased to nine guns in three non-superfiring triple-gun turrets,McLaughlin, p. 245 based on a false rumour that the Germans were increasing the calibre of the guns in their battleships.Budzbon, p. 304 The Imperial Russian Navy believed that widely separating the main gun turrets and their magazines reduced the chance of a catastrophic ammunition explosion, reduced the silhouette of the ship and improved stability without superfiring turrets and their tall barbettes.McLaughlin, pp. 212–213
The Naval Ministry solicited new bids on 8 September from 23 shipbuilders, domestic and foreign, but only 7 responded, even after the deadline was extended by a month. Several designs were rejected for not meeting the revised criteria. In the meantime, the Artillery Section of the Main Administration of Shipbuilding had decided that it preferred a four-turret design, and new bids were solicited in May 1912 from the leading contenders from the first round of bidding. The eventual winner was a design by the Admiralty Shipyard in Saint Petersburg which had the extra turret added to a new hull section inserted into the original three-turret design.McLaughlin, pp. 245–246
The Duma approved construction in May 1912, before the design was finalised, and allocated 45.5 million roubles for each ship. The additional gun turret and consequent increase in the size of the ships led to the ships being overbudget by about 7 million roubles each, and some money was diverted from the budget for the to cover the discrepancy. Orders were placed on 18 September 1912 for a pair of ships each from the Admiralty Shipyard and the Baltic Works, also of Saint Petersburg. The first pair was to be ready for trials on 14 July 1916, and the second pair on 14 September 1916.Watts, p. 65McLaughlin, p. 247
Full-scale armour trials in 1913 revealed serious weaknesses in the Borodinos' proposed protection scheme. The obsolete ironclad had been modified with armour protection identical to that used by the s, then under construction. The deck and turret-roof armour proved to be too thin, and the structure supporting the side armour was not strong enough to withstand the shock of impact from heavy shells. The design of the Borodinos' armour was similar in construction to that of the Ganguts and therefore needed to be modified, which slowed construction. The Borodinos' deck armour was reinforced with extra plates and the thickness of the turret roofs was increased. To offset this additional weight, a planned rear conning tower was removed entirely and the thickness of the main belt was slightly reduced. Mortise and tenon joints were introduced between the armour plates along their vertical edges to better distribute the shock of a shell impact and to lessen the stress on the supporting hull structure. The launching of the first pair of ships was postponed by six months because of these changes, plus delays imposed by the many ship orders already in hand.McLaughlin, pp. 247–248
General characteristics The Borodino-class ships were long overall. They had a beam of and a draught of at full load. The ships displaced normally and at full load.Taras, p. 39 High-tensile steel was used throughout the hull with mild steel used only in areas that did not contribute to structural strength. The hull was subdivided by 25 transverse watertight bulkheads and the engine room was divided by a longitudinal bulkhead. The double bottom had a height of , and the vitals of the ship were protected by a triple bottom that added an extra of depth. The design called for a freeboard of forward, amidships and aft. The ships were fitted with three Frahm anti-rolling tanks on each side.McLaughlin, pp. 243, 249, 251
Propulsion The Borodinos were powered by four sets of steam turbines, each driving one propeller shaft using steam provided by 25 triangular Yarrow boilers with a working pressure of . The turbines developed a total of and were designed to be overloaded to . The forward boilers were grouped into three compartments with three oil-fired boilers in each compartment. The rear boilers were in four compartments with each containing four coal-fired boilers fitted with oil sprayers to increase the burn rate. Maximum speed was estimated at 26.5 knots, although forcing the machinery would increase it to . The ships were designed to carry of coal and of fuel oil, which gave an estimated range of at full speed.McLaughlin, pp. 244, 253–254
Two sets of steam turbines were ordered on 22 April 1913 from the Franco-Russian Works in Saint Petersburg for the Admiralty Shipyard-built ships, and the Baltic Works built the turbines for its ships, although some components were ordered from abroad.McLaughlin, p. 253, especially footnotes 28 and 29 However, Western sources have long stated incorrectly that the turbines for Navarin had been ordered from AG Vulcan, and that they were taken over at start of the war for use in the light cruisers. As well as being contradicted by original Russian and German records, this is technically impossible, as the turbines actually specified for Navarin were of the Parsons type, while those actually employed in the German cruisers were of the Curtis pattern. In fact, the Brummer class engines had been ordered for the lead ship of the Svetlana-class cruisers.Dodson & Nottelmann, p. 190
The Borodino class had six turbo generators and two diesel generators, each rated at . These were in four compartments below the main deck, two each fore and aft of the boiler and engine rooms. The generators powered a complex electrical system that combined alternating current for most equipment with direct current for heavy-load machinery such as the turret motors.McLaughlin, pp. 254, 332
Armament The ships' primary armament consisted of a dozen 52-calibre Model 1913 guns mounted in four electrically powered turrets. The turrets were designed to elevate and traverse at a rate of 3° per second. The guns had an elevation range from −5° to +25°. They could be loaded at any angle between −5° and +15°; the expected rate of fire was three rounds per minute. Space was provided for a maximum of 80 rounds per gun. The guns fired projectiles at a muzzle velocity of , with a maximum range of .McLaughlin, pp. 251–252
The secondary armament consisted of twenty-four 55-calibre Pattern 1913 guns mounted in casemates in the hull, twelve per side.McLaughlin, p. 252 The guns had a maximum elevation of +20° which gave them a range of . They fired projectiles at a muzzle velocity of .Friedman 2011, p. 262
The anti-aircraft armament was intended to be four 38-calibre anti-aircraft guns fitted on the upper deck with 220 rounds carried for each gun. They fired projectiles at a muzzle velocity of .Friedman 2011, pp. 264–265 Four guns were to be mounted in pairs on the main turret roofs for sub-calibre training with the main guns. Six underwater torpedo tubes were fitted, three on each broadside; they were provided with a total of eighteen torpedoes.
Fire control The fore and aft main gun turrets were given a rangefinder, and there was another unit on top of the conning tower. These would provide data for the Geisler central artillery post analogue computer, which would then transmit commands to the gun crew.Friedman 2008, pp. 273–275 The mechanical fire-control computer would have been either a Pollen Argo range clock, which had been bought in 1913, or a domestically designed Erikson system.
Protection The trials with Chesma greatly affected the armour protection design of the Borodino-class ships. The Krupp cemented-armour plates were resized to match the frames and provide support for their joints; they were also locked together with mortise-and-tenon joints to better distribute the shock of a shell's impact. The waterline belt covered the middle of the ship. It had a total height of , of which was above the design waterline and below. The remaining portion of the waterline was protected by plates. The upper belt was thick and had a height of . It thinned to 75 millimetres forward of the casemates and extended all the way to the bow. The rear portion of the forecastle deck was protected by an upward extension of the upper belt in the area of the forward barbettes and the upper casemates. Those casemates were protected by 100-millimetre transverse bulkheads. Behind the side armour was an inboard longitudinal splinter bulkhead that was thick between the middle and lower decks and decreased to between the middle and upper decks. The bulkhead sloped away from the edge of the lower deck to the lower edge of the armour belt with a total thickness of 75 millimetres divided between a 50-millimetre plate of Krupp non-cemented armour (KNC) layered above a 25-millimetre nickel-steel plate. The forward end of the armoured citadel was protected separately and the transverse bulkhead was therefore only 75 millimetres thick. The rear bulkhead had no other protection and was thick between the middle and lower decks, decreasing to 75 millimetres at the level of the armour belt.