MO-class small guard ship

The MO-4-type patrol boat SKA-065 during World War II
Class overview
Name	MO class
Operators	Soviet Navy  Soviet Border Troops
Succeeded by	OD-200 class
Subclasses	MO-1, MO-2, MO-3, MO-4, BMO
Built	1935–1945
In service	1935–1945
Completed	350+
General characteristics (MO-4 type)
Type	Patrol boat / submarine chaser
Displacement	50.6 tonnes (49.8 long tons; 55.8 short tons) standard 56.5 tonnes (55.6 long tons; 62.3 short tons) full load
Length	26.9 m (88 ft 3 in)
Beam	4.02 m (13 ft 2 in)
Draught	1.35 m (4 ft 5 in)
Propulsion	3 × GAM-34BS engines Total power: 2,550 PS (2,520 shp; 1,880 kW)
Speed	26 knots (48 km/h) to 27.4 knots (50.7 km/h)
Complement	22 men
Armament	2 × 45 mm (1.8 in) 21-K guns 2 × 12.7 mm (0.50 in) DShK machine guns 2 depth charge racks (8 depth charges)

The MO (Russian: МО, an initialism for Малый охотник, Malyj okhotnik, 'Small Hunter'; nickname Мошка, Moshka, 'Midge') is a class of naval boats produced before and during World War II for the Soviet Navy and NKVD Border Troops. Their primary function originally was anti-submarine warfare. During the war they carried out many additional roles from supporting landing operations to escorting convoys. Over 350 boats were built.^[1]

In early 1930s, the main focus of Soviet shipbuilding was building small patrol ships and boats with various duties. Among them, a large part consisted of submarine hunter boats. The MO class was the first Soviet built submarine hunter boat class, with the abbreviation meaning "Small Hunter". Unlike torpedo boats, MO boats had no torpedo weapons, but instead had depth charge racks.^[1]

The lead ship of the class was a 51 tonnes (50 long tons; 56 short tons) border patrol boat PK-139, which was given the class designation of MO-1 in 1935. The production series was a slightly faster boat, given the designation MO-2. Some 27^[1] to 36^[2] boats of this class were built in 1935–1936. A slightly modified MO-3 was in limited production resulting in four boats built.^[1]

MO-4 was the most produced type of the class, with approximately 250 built. It was a slightly modified MO-2 variant, with a more vertical stern and slightly lower. It was designed at the Design Bureau of NKVD Maritime Border Guard Shipyard in Leningrad (from 1939 known as the NKVD's Factory No. 5, now the Almaz Shipbuilding Company). The boat had no armor and had a wooden structure, but consisted of nine sections isolated from each other, allowed to stay afloat even after suffering heavy damage. Three GAM-34BS gasoline engines had a power of 850 metric horsepower (840 shp; 630 kW) at 1,850 rpm or 675 PS (666 shp; 496 kW) at 1,750 rpm. The main weapons of the boat were the depth charges and 45 mm semi-automatic guns. The boats also had a pair of DShK heavy machine guns. MO-4 boats were built at several shipyards including Leningrad, Sosnovka and Astrakhan from 1937 to 1943.^[1]

In summer 1943, the Leningrad shipyards designed a new variant to remedy the MO-4's lack of armor. The letter B stood for bronirovannyj (Russian: бронированный, lit. 'armored'). The new boat was made of steel, with armor of up to 12 mm (0.47 in) protecting the engine. One of the 45 mm guns was replaced with a 37 mm 70-K anti-aircraft gun, which had higher performance in the anti aircraft role. 48 were built during the war and another 18 in the second half of 1945.^[3][4]

MO-class boats carried out a very large number of duties during the war, serving in all fleets. Their duties included patrolling naval bases perimeter, hunting submarines, escorting convoys, laying and disarming mines, supporting amphibious landings and fighting small enemy ships. Some distinguished individual boats are listed below.^[1][2]

This is one of the most famous MO-4-type boats. On July 30, 1944 she sank the German submarine U-250 in shallow waters of the Baltic Sea. The commander of U-250 and five crewmen survived and were captured. The submarine was raised by Soviet forces in early September and moved to Leningrad. To the delight of the engineers, the submarine had intact secret acoustic torpedoes on board.^[1][5]

The MO-4-type boat was earlier named MO-113. Sank the German submarine U-679 on January 9, 1945 in the Baltic Sea.^[6]

The MO-4-type boat was earlier known as PK-125 (while serving in the NKVD Border Troops), SKA-074 and SKA-065 (while serving in the Soviet Navy). The boat was mobilized by the Black Sea Fleet during the Great Patriotic War and it was named the "Guards Boat" on July 25, 1943 for distinguished services in battle (Commanding Officer, Senior Lieutenant Pavel Sivenko, received a lot of Soviet military decorations and was also awarded the Navy Distinguished Service Medal of the United States).^[7] Survived until the end of the war and was returned to the NKVD Border Troops in July 1945.^[8]

The MO-4-type boat was earlier named PK-148 (while serving in the NKVD Border Troops). She was mobilized by the Black Sea Fleet during the Great Patriotic War. The boat destroyed two enemy patrol boats and one aircraft during wartime. The boat also escorted a total of 184 ships on convoying missions and removed 20 sea mines during mine sweeping missions. SKA-084 was the first boat in the Soviet Navy to have the naval 82 mm (3.2 in) Katiusha variant installed. Sunk by artillery fire on September 11, 1943 near Novorossiysk.^[9]

• Боевые корабли России [Military Ships of Russia] (in Russian). Parus. 1996. ISBN 5-89410-001-1.
• Чернышев И. П. [Chernyshev I. P.] (1981). О друзьях-товарищах (in Russian). Лениздат.
• Сорокин А. И. [Sorokin A. I.]; Краснов В. Н. [Krasnov V. N.] (1985). Корабли проходят испытания (in Russian). Судостроение.

Wikimedia Commons has media related to MO-class subchaser.

• "Black Sea Fleet website" (in Russian).