In the mid-1950s, the Soviet Union began developing a new diesel-electric icebreaker design based on the 1942-built steam-powered icebreaker
Eisbär to meet the needs of both civilian and naval operators. Built in various configurations until the early 1980s, the
Project 97 icebreakers and their derivatives became the largest and longest-running class of icebreakers and icebreaking vessels built in the world. The patrol ship variant, Project 97P (), was developed as a response to the renewed interest of the Soviet Navy and
Soviet Border Troops on icebreaking patrol vessels after
United States Coast Guard and
Canadian Coast Guard icebreakers began appearing more frequently near the country's northern maritime borders. New icebreaking patrol vessels were needed because existing Soviet naval vessels could not operate in ice-covered waters and large icebreakers, in addition to being unarmed and operated by civilians, could not be distracted from their primary mission of escorting merchant ships. Project 97P patrol ships are
long overall and have a beam of . Fully laden, the vessels draw of water and have a displacement of . Their three
10-cylinder 13D100
two-stroke opposed-piston diesel engines are coupled to generators that power electric propulsion motors driving two propellers in the stern. In addition to being slightly bigger than the icebreakers they are based on, Project 97P lacks the bow propeller and features a bigger deckhouse built of aluminum-magnesium alloy to reduce weight as well as a helideck capable of receiving
Kamov Ka-25 or
Ka-27 helicopters. All Project 97P patrol ships were initially armed with a twin 76 mm
AK-726 deck gun and two 30 mm
AK-630 close-in weapon systems, but the ships operated by the navy were later disarmed. == History ==