The main armament of the "Petropavlovsk" class consisted of four 40-caliber 12-inch guns mounted in twin-gun turrets fore and aft of the superstructure. They used hydraulic power for loading and traversing, but the ammunition hoists were electrically powered. Designed to fire one shell every 90 seconds, the rate of fire of the guns in service proved to be one round every three minutes. The structure of the turrets proved to be too weak to withstand extra-strength charges and had to be reinforced. The guns could elevate to a maximum of +15° and traverse 270°; each was provided with 58 rounds. They fired a shell at a muzzle velocity of . This gave them a range of at an elevation of 10°.