Kronshtadt Class Battlecruiser - Design

Design

The Kronshtadt-class battlecruisers had their origin in a mid-1930s requirement for a large cruiser (Russian: bol'shoi kreiser) capable of destroying 10,000-long-ton (10,160 t) cruisers built to the limits imposed by the Washington Naval Treaty, to 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 23,000 metric tons (22,637 long tons) and armed with 254-millimeter (10.0 in) 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 35,000 long tons (35,562 t). 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 34 knots (63 km/h; 39 mph) and an armament of nine 254 mm guns, but the requirement proved to be too ambitious for the specified size and it increased to 26,200 metric tons (25,786 long tons) in the design submitted in June 1938. By this time, however, details were becoming available for the Scharnhorst-class battleships and the ship was deemed inferior to the German ships. The State Defense Committee revised the requirements and specified a size about 31,000 metric tons (30,510 long tons), an armament of nine 305-millimeter (12.0 in) guns, an armor belt 250 mm (9.8 in) thick and a speed about 31–32 knots (57–59 km/h; 36–37 mph). A revised design was finished by October which was wargamed against the Japanese Kongō-class battlecruisers, the French Dunkerque-class battleships 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 Kongos as rebuilt or of the Scharnhorsts as the displacement of the latter had been given as 26,000 metric tons (25,589 long tons), more than 5,000 metric tons (4,921 long tons) short of their true displacement. The Navy's Shipbuilding Administration thought that the original secondary armament of 130-millimeter (5.1 in) 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 152-millimeter (6.0 in) 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 500-kilogram (1,100 lb) bomb would penetrate both a 40-millimeter (1.6 in) upper deck and a 50-millimeter (2.0 in) middle deck to burst on the main armor deck. So the middle deck was thickened to 90-millimeter (3.5 in) with the lower deck intended to catch any splinters penetrating the armor deck. This mean 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 283-millimeter (11.1 in) 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 380-millimeter (15.0 in) 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 10-meter (33 ft) rangefinders and 150-centimeter (59 in) 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 was bigger in diameter than that of the 305 mm turret as well as 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 37-millimeter (1.5 in) anti-aircraft guns behind turret number three had to 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 1,000 metric tons (984 long tons) 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.