During the summer of 1937, the Soviet government made a number of important maritime policy decisions. On July 17, 1937, an Anglo-Soviet naval agreement was signed to define the qualitative limitations for the major categories of ships. On August 13/15, a government decree was issued initiating the revision of the Major naval shipbuilding program of 1936. The new plan called for a reduction in the number of battleships and an increase in the number of destroyers, with the fleets to be reinforced with heavy cruisers and aircraft carriers. The «Warship building plan for the Soviet Navy» was not officially adopted, though on November 1, 1937 the People's Commissariat for the Defense Industry received the «Design specifications for a Project 69 heavy cruiser». The ship was primarily designed to counter enemy cruisers, provide support to light forces involved in active operations in remote areas, and act individually on the enemy communication routes.
The initial design implied the use of 254 mm main battery guns, a water displacement of 20–23 thousand tons, a speed of at least 34 knots and an economic cruising range of 8,000 miles. At first, the cruiser was to carry nine 254 mm guns mounted in three-gun turrets and eight 130 mm guns in twin turrets. The ship's AA defenses comprised eight 100 mm guns and sixteen 37 mm automatic machine guns. Apart from that, the cruiser was to be equipped with two triple torpedo launchers.
However, when the information about the completion of construction of Scharnhorst-class battleships became known, a new combat objective was added for the Project 69 heavy cruiser—countering the new German warships. Central Design Bureau No.17 (TsKB-17) commenced work on a ship designed to bear 305 mm main guns, an armor belt of 230 mm, a 32,500-ton water displacement, and a speed of 32 knots. However, in the early stages of the ship's design, the Military Council of the Navy approved the proposal of the People's Commissariat for the Defense Industry to exclude torpedoes from the cruiser's armament. On July 10, 1938, the updated «Principal design specifications for a heavy cruiser designed for the needs of the Soviet Navy» were approved. The draft and technical designs of the heavy cruiser were approved by the government on July 1939 and April 1940, respectively.
According to the last pre-war program for the development of the Navy—a five-year shipbuilding plan for 1938–1942—a total of four heavy cruisers were to be laid down under Project 69. The keel-laying ceremony of the lead cruiser designated «Kronshtadt» was, in fact, held on November 30, 1939 at Leningrad Shipyard No. 194 in the name of André Marti (currently, Admiralty Shipyards). A second ship in the series named «Sevastopol» was laid down at Shipyard No. 200 in the name of 61 Communards (currently, Mykolayiv Shipyard) at an even earlier date, on November 5. The ships were to be handed over to the Navy in 1943.
On August 1, 1940, the People's Commissar for the Navy approved the design specifications for a project to re-arm Kronshtadt and Sevastopol with German 380 mm turret guns. The decision stemmed from the trade deal signed by Germany and the Soviet Union on February 11, 1940 for the delivery to the U.S.S.R. of six 380 mm twin-gun turrets equipped with a Siemens fire director. Moreover, the development of the Soviet MK-15 turrets was proceeding at an extremely slow rate. The updated project was designated «69I».
On October 9, 1940, the People's Commissar and Chief of the Soviet Naval Forces Kuznetsov sent a letter to Voroshilov, the Chairman of Defense Committee under the Council of People's Commissars, stating as follows: «To avoid a troublesome situation that could occur if Germany refused to deliver their main gun turrets, the People's Commissariat for Shipbuilding and the People's Commissariat for the Navy consider it expedient not to discontinue work on the «old» draft designs intended for the heavy cruisers, which should be developed in parallel with the ongoing projects adopted for the German turrets." The agreements for the delivery of the guns and fire directors were signed with the supplying firms, Krupp and Siemens, on November 30 and December 23, 1940, respectively. In practice, however, Germany never furnished any set of work documentation for the armaments supplied. The ships' construction process was, therefore, slow, with no work commenced at all on the parts where the turrets were to be mounted.
As of June 21, 1941, Kronshtadt's construction had progressed to the lower deck, beds for the main machinery were installed, sections of the double bottom and mine protection were tested for watertight integrity, and the assembling of bulkheads between the lower and middle decks was commenced. The double bottom section was installed and riveted. Four mine protection fore-and-aft bulkheads were completed. Processing of the armored plates for the lower deck was finished.
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On July 10, 1941, the State Committee for Defense issued a resolution to suspend all work on the construction of the heavy cruisers under Project 69 with the ships' hulls subject to preservation. On August 16, 1941 the city of Mykolaiv was occupied by German forces, Sevastopol's hull was partially disassembled and taken to Germany. During the blockade of Leningrad, a large number of armored steel plates were removed from Kronshtadt to be used in the construction of various defense facilities. In 1947, when the war was over, the remains of both ships' hulls were scrapped.
Technical specifications of the Project 69 heavy cruiser
The cruiser was to have a flush-deck hull design, slightly flared, with bulges in the middle section of the hull. The projected frame spacing was 500 mm but the actual frame spacing reached 750 mm. The hull was divided by watertight bulkheads into eight compartments.
The main armor belt was made of 230 mm cemented armor plates installed with an outward flare of 5 degrees. The upper edge of the side plates was attached to the middle armored deck and the lower edge was placed on a special armor shelf. The splinter belt in the ship's bow was made of 20 mm plates of homogeneous armor. The upper deck was protected by 14 mm plates of homogeneous armor. The middle deck, or the main armored deck that was located around the citadel, was protected with 90 mm plates of homogeneous armor, while the lower deck was protected with 30 mm plates. The fore and aft athwartship bulkheads were made of 330 mm and 275 mm cemented armor plates, respectively.
30-millimeter splinter-proof athwartship bulkheads made from homogeneous armor were used to defend the sections located beneath the main gun turrets from shell splinters. The barbettes of the main gun turrets were covered with 330 mm cemented armor plates placed above the middle deck. In the area between the middle and lower decks, the barbettes were protected with 30 mm homogeneous armor plates. The barbettes of the MK-17 secondary battery turrets were made of 75 mm plates of homogeneous armor sidewards and 50 mm plates on the centerline. The barbettes of the long-range AA gun turrets were made of 40 mm plates of homogeneous armor.
The MK-15 main gun turrets were protected as follows: front and rear parts were protected with 305 mm cemented armor, and the sides and top with 125 mm homogeneous armor. Secondary battery turrets were protected with a 100 mm front plate, 50 mm plates on the sides, a 110 mm plate in the rear and a 50 mm plate on top. The long-range AA gun turrets were protected with 50 mm front, side, and top plates while the rear part of the turret was protected with a 70 mm plate.
The conning tower had 330 mm of cemented armor protection on the front, and 250 mm and 275 mm of armor protection on the sides and the rear, respectively. 125-millimeter plates were used to cover the top of the conning tower.
The depth of mine protection for the cruiser ranged from 4 m near the fore and aft magazines, to 6 m amidships. The sides of the ship were protected against mines with four 20 mm, 20 mm, 16 mm, and 16 mm fore-and-aft steel bulkheads.
The cruiser's main battery is composed of three MK-15 three-gun turrets housing 305 mm guns (B-50). Gun elevation angles: −3 to +45 degrees. Elevation aiming speed: 5.1 degrees per second. Rate of fire: 3.2 to 2.36 shots per minute depending on the angle of elevation. Maximum firing range: 52 km (for AP shells) and 47 km (for HE shells). Shell muzzle velocity: 900 m/s (for AP shells) and 920 m/s (for HE shells).
The secondary battery included four MK-17 two-gun turrets (an MK-4 turret with lighter armor protection compared to Project 23) housing B-38 guns (152 mm). The ship's long-range AA defenses included four two-gun MZ-16 turrets, a slightly altered MZ-14 turret with lighter armor protection compared with Project 23, and 100 mm guns (B-34). Small-caliber anti-aircraft armament included seven 46-K quadruple 37 mm automatic air defense guns.
Aircraft-handling equipment comprised a catapult and two KOR-2 flying boats hoisted on the ship's deck.
Gun Fire Control Systems
The cruiser's main gun fire control equipment was mounted in two central gunfire control stations and included two KDP-2-8 (B-41) directors and three 12-meter turret range finders. The secondary battery and long-range AA guns were controlled via two KDP-2-4 (B-42) directors and three SPN-300 stabilized laying stations, respectively.
The propulsion system was based on the same power units that were used on Sovetsky Soyuz-class battleships and included three main turbine plants with 70,000 hp each.