Kronshtadt-class battlecruiser

Planned class of Soviet battlecruisers

The Kronshtadt class battlecruisers, with the Soviet designation as Project 69 heavy cruisers ("Тяжёлые крейсера проекта 69"), were ordered for the Soviet Navy in the late 1930s. Two ships were started but none were completed due to World War II. These ships had a complex and prolonged design process which was hampered by constantly changing requirements and the Great Purge in 1937. They were laid down in 1939, with an estimated completion date in 1944, but Stalin's naval construction program was more ambitious than the shipbuilding and armaments industries could handle. Prototypes of the armament and machinery had not even been completed by 22 June 1941, almost two years after the start of construction. This is why the Soviets bought twelve surplus SK C/34 guns, and their twin turrets, similar to those used in the s, from Germany in 1940. The ships were partially redesigned to accommodate them, after construction had already begun, but no turrets were actually delivered before Germany invaded the following year. Only Kronshtadts hull survived the war reasonably intact being 10% complete in 1945, although she was considered to be obsolete. The Soviets considered converting her into an aircraft carrier, but the idea was rejected and both hulls were scrapped in 1947.

The Kronshtadt class battlecruisers had their origin in a mid 1930s requirement for a large cruiser (bol'shoi kreiser) capable of destroying cruisers built to the limits imposed by the Washington Naval Treaty, of which the Soviets were not a signatory. Several designs were submitted by the end of 1935, but the Navy was not satisfied and rejected all of them. It asked for another design, displacing and armed with guns, in early 1936, eventually designated Project 22, but this design was cancelled after the Soviets began negotiations in mid 1936 with the British that ultimately resulted in the Anglo Soviet Quantitative Naval Agreement of 1937 and agreed to follow the terms of the Second London Naval Treaty which limited battleships to a displacement of The Soviets had been working on a small battleship design (Battleship 'B') for service in the Baltic and Black Seas and had to shrink it as a result of these discussions to a size close to that of the Project 22 large cruiser so that the latter was cancelled. Battleship 'B' was redesignated as Project 25 and given the task of destroying Treaty cruisers and German pocket battleships. The Project 25 design was accepted in mid 1937 after major revisions in the armor scheme and the machinery layout and four were ordered with construction to begin in late 1937 and early 1938. However, this decision occurred right before the Great Purge began to hit the Navy in August 1937 and two of the ship's designers were arrested and executed within a year. The Project 25 design was then rejected on the grounds that it was too weak compared to foreign ships and the whole program was cancelled in early 1938 after an attempt to modify the design with larger guns had been made. However the Soviet Navy still felt a need for a fast ship that could deal with enemy cruisers and the original concept was revived as Project 69. They wanted a ship not to exceed 23,000 metric tons with a speed of and an armament of nine 254 mm guns, but the requirement proved to be too ambitious for the specified size and it increased to in the design submitted in June 1938. By this time, however, details were becoming available for the s and the ship was deemed inferior to the German ships. The State Defense Committee revised the requirements and specified a size about , an armament of nine guns, an armor belt thick and a speed about A revised design was finished by October which was wargamed against the Japanese s, the French s as well as the Scharnhorst class. It was deemed superior to the Kongos at medium range and inferior to the Dunkerques at the same range, but generally superior to the Scharnhorsts, although it is doubtful that the Soviets were fully aware of the true specifications of the Kongōs as rebuilt or of the Scharnhorsts as the displacement of the latter had been given as , more than short of their true displacement. The Navy's Shipbuilding Administration thought that the original secondary armament of guns was too small and that the armor on the turrets, conning tower and the forward transverse bulkhead was too thin. A revised, 35,000 ton design with guns and extra armor was submitted to the State Defense Council in January 1939. This was approved and the detailed design work began with the basic concept that the ship should be superior to the Scharnhorst class ships and able to outrun the Bismarck class battleships. At this time the horizontal protection was revised after full scale trials revealed that a bomb would penetrate both a upper deck and a middle deck to burst on the main armor deck. So the middle deck was thickened to with the lower deck intended to catch any splinters penetrating the armor deck. This meant that the main belt had to be extended upwards to meet the main armor deck at a significant penalty in weight. The Defense Committee approved the sketch design on 13 July 1939, but the detailed design was not approved until 12 April 1940, after construction had already begun on the first two ships. It was already apparent that the 305 mm guns and turrets were well behind schedule when Joseph Stalin asked the German representatives in Moscow on 8 February 1940 to negotiate a trade agreement if it would be possible to use the triple turrets in lieu of the triple 305 mm turrets of the Project 69 ships. They replied that the turrets were out of production, but new ones could be built. He then asked if twin turrets could be used instead. The Germans said that they would have to check back for the technical details. Krupp had six incomplete turrets on hand that had originally been ordered before the war to rearm the Scharnhorst class battleships, but they were cancelled after the start of World War II when the Germans decided that they could not afford to have the ships out of service during the war. A preliminary purchase agreement was made to buy twelve guns and six turrets later that month, well before any studies were even made to see if the substitution was even possible. The Shipbuilding Commissariat reported on 17 April that it was possible so the agreement was finalized in November 1940 with the deliveries scheduled from October 1941 to 28 March 1943. The order also included rangefinders and searchlights. The Soviets never did get the detailed data required to redesign the ship's barbettes and magazines, but they did know that the 380 mm barbettes were bigger in diameter than that of the 305 mm turret as well as being taller than the Russian turrets. So the barbette of turret number two had to be raised to clear turret number one and the height of the conning tower had to be raised to clear turret number two. Similarly the anti aircraft guns behind turret number three had to be raised as well. The new turrets required more electrical power which meant that the output of the turbo generators had to be increased to 1,300 kilowatts. All of these changes added over to the ships' displacement and the sketch design was completed by 16 October 1940, as Project 69 I (Importnyi—Imported), even though they still lacked data for the turrets and their barbettes. This was presented to the State Defense Committee on 11 February 1941, but the design was not approved until 10 April when it ordered that the first two ships be completed with German guns while the others would continue to use the 305 mm guns. The detailed design was supposed to be completed by 15 October 1941, but it was rendered pointless when the Germans invaded the Soviet Union in June. The hull form was very full with a block coefficient of 0.61 which compared badly to the 0.54 of the Dunkerque, the 0.52 of the German or the 0.5266 of the American This meant that a lot of horsepower was necessary to achieve even modest speeds. Stalin's decision that the Project 69 ships would use three shafts increased the shaft loading and reduced propulsive efficiency, although it did shorten the length of the armored citadel and thus overall displacement. The riveted hull was subdivided by 24 transverse bulkheads and used longitudinal framing in the citadel, but transverse framing for the structure fore and aft of the citadel. The metacentric height was for the 305 mm gunned ships, but dropped to in the 380 mm gunned ships. The tactical diameter was estimated at about
The Kronshtadt class ships were provided with two KOR 2 flying boats which would be launched by the catapult mounted between the funnels. Maximum speed was estimated at , using the revised propeller design, although forcing the machinery would yield an extra knot. The normal fuel oil capacity was , which provided an estimated endurance of at full speed. Maximum fuel capacity was which gave a range of at and at .

The main armament was initially going to consist of three electrically powered triple gun turrets, each with three 54 caliber 305 mm B 50 guns. The turrets were based on the MK 2 turrets planned for the Project 25 large cruiser. The guns could be depressed to −3° and elevated to 45°. They had a fixed loading angle of 6° and their rate of fire varied with the time required to relay the gun. It ranged from 2.36 to 3.24 rounds per minute depending on the elevation. The turrets could elevate at a rate of 10 degrees per second and traverse at 5.1 degrees per second. 100 rounds per gun were carried. The gun fired armor piercing projectiles at a muzzle velocity of ; this provided a maximum range of
The secondary armament consisted of eight 57 caliber B 38 152 mm guns mounted in four twin gun turrets concentrated at the forward end of the superstructure. The forward turrets were inboard and above the outer turrets which provided both turrets with good arcs of fire. Their elevation limits were 5° to +45° with a fixed loading angle of 8°. Their rate of fire also varied with the elevation from 7.5 to 4.8 rounds per minute. The turrets could elevate at a rate of 13 degrees per second and traverse at 6 degrees per second. They had a maximum range of with a shell at a muzzle velocity of
Heavy anti aircraft (AA) fire was provided by eight 56 caliber 100 mm B 34 dual purpose guns in four twin turrets mounted at the aft end of the superstructure with the aft turrets mounted inboard of the forward turrets. They could elevate to a maximum of 85° and depress to 8°. Light AA defense was handled by six quadruple, water cooled mounts fitted with 70 K guns. Two mounts were abreast the forward funnel, two just abaft the rear funnel and the last two on the centerline of the aft superstructure superfiring over the rear main gun turret. Initially seven mounts were planned, but the one above the conning tower was exchanged for a director for the 100 mm guns in early 1940 when the Navy realized that the other directors were blocked by the superstructure. The guns fired shells at a muzzle velocity of Their maximum range was
The Germans sold the Soviets twelve 52 caliber SKC/34 guns and their associated Drh LC/34 turrets as part of the Molotov–Ribbentrop Pact.

Two KDP 8 III fire control directors were used to control the main armament. These had two stereoscopic rangefinders, one to track the target and the other to measure the range to the ship's own shell splashes. Two of these were protected by of armor and were mounted atop the rear superstructure and the tower mast. Two KDP 4t II directors, with two rangefinders each, controlled the secondary armament. The dual purpose guns were controlled by two, later three, stabilized directors, each with a rangefinder. Machinery problems were likely to delay the ships well past their intended delivery dates of 1943–44. The Kharkhovskii Turbogenerator Works never completed a single turbine before the German invasion in June 1941. Another problem were the 305 mm guns and turrets as the armament factories were focused on the higher priority guns for the Sovetsky Soyuz class battleships. Prototypes of neither had been completed by the time the Germans invaded. The situation was not much better for the smaller guns as mountings for both the 152 mm and 100 mm guns were still incomplete on 22 June 1941 and all of these programs were terminated quickly afterwards.

The ships were originally intended to be laid down 1 September 1939, but they were delayed until November to allow improvements to the shipyards to be completed. A total of sixteen ships were planned in the August 1939 building program, but this was scaled back to four in July 1940 and two in October 1940 when it became clear just how unprepared the Soviets were for any large scale naval construction program. Work on these ships ceased shortly after the German invasion. Kronshtadt (Кронштадт) was built by the Shipyard No. 194, Marti in Leningrad. She was laid down 30 November 1939 and judged 10.6% complete when the Germans invaded. Her building slip was too short for her entire length so her stern was built separately. Some of her material was used during the siege of Leningrad to repair other ships and in defensive works, but she could have been finished after the end of the war. Proposals were made to complete her as an aircraft carrier and as a base ship for a whaling flotilla, but both ideas were rejected and she was ordered scrapped on 24 March 1947. Her dismantling began shortly afterwards and was completed the following year. Sevastopol (Севастополь) was built by Shipyard No. 200, 61 Communards in Nikolayev. She was laid down on 5 November 1939 and estimated as 11.6% complete on 22 June 1941. She was captured by the Germans when they occupied Nikolayev in late 1941, but the Germans did little with her other than to use some of her material for defensive positions and some was apparently shipped to Germany. Before the Germans evacuated the city they damaged her building slip and hull with explosives and made her a constructive total loss. She was ordered scrapped on 24 March 1947 and her dismantling began shortly afterwards. It was completed in 1948.