In 1935, new international challenges forced the U.S.S.R. to adjust their ship building policy, which until that point had not paid enough attention to battleships as a ship type. These changes gave the design bureaus a green light to initiate the development of a number of draft designs for battleships. In 1936, the design performance specifications were prepared. Project 21, the design for a battleship intended to operate in the Baltic Sea, was developed by the Design Bureau of the Baltic Shipyard on the basis of the provided performance specifications. These were: water displacement of 35,000 tons; a main battery comprising nine 406 mm guns; and an armor belt 350 mm thick. The draft design was ready by June. The arrangement of the ship’s main turrets was similar to that of British battleship Nelson, with three turrets placed at the fore-end. The ship also carried 152 mm secondary battery guns and long-range 100 mm AA guns. The engineers applied the Italian-designed Pugliese torpedo defense system. However, the Nelson-like layout was rejected by Naval Command after heated debates due to "tactical reasons". The experience gained during the development of Project 21 was used as the basis for the "Type A Battleship" project that later evolved into the Sovetsky Soyuz-class battleship.