During the Great Patriotic War, not only multiple launch rocket systems were called "katyushas," but also the largest and fastest Soviet submarines - submarine cruisers of the K. It was on the Red Banner "K-21" Hero of the Soviet Union N.A. Lunin attacked the flagship Kriegsmarine battleship Tirpitz; on mines delivered by "K-1," 8 enemy ships and vessels were blown up - the best result among the underwater barriers of our fleet - and in total on the account of "Katyusha" more than 30 victories. However, these successes had to pay a high price - out of thirteen squadron and cruiser submarines, six did not return from military campaigns. Whose fault was the loss so high? Why, after two failures, submarines of type P were actually put on joke, and the effectiveness of Katyusha in torpedo attacks left much to be desired? What mistakes were made at the design and construction stage? And what else has been hushed up for more than half a century? All these questions are answered by a new book by leading fleet historians, which has become the result of many years of research in domestic and foreign archives.