The 'Battle of the Black Sea' is a designation which covers the naval campaign waged between the Axis and Soviet naval forces in the Black Sea and its coastal regions (22 June 1941/August 1944).

Vitse Admiral Filipp S. Oktyabrsky’s Soviet Black Sea Fleet was taken by surprise as much as the other Soviet forces by the start of the 'Barbarossa' invasion launched by Germany and its allies on 22 June 1941. The Axis forces in the Black Sea comprised the Romanian and Bulgarian navies, together with German and Italian units transported to the area via rail and canal. Although the Soviets enjoyed an overwhelming superiority in surface ships over the Axis, this was effectively negated by German air superiority and most of the Soviet ships sunk were sunk by bombing. For the majority of the war, the Black Sea Fleet was commanded by Oktyabrsky until he was succeeded by Vitse Admiral Lev A. Vladimirsky in May 1943.

The major Soviet shipyards were located ay Nikolayev in Ukraine and Sevastopol on the Crimean peninsula. The former was occupied by Germany in 1941, but although the latter was not occupied until July 1942, the rest of Crimea were also occupied in 1941, rendering the shipyards largely unusable. Many ships which were afloat but incomplete were evacuated to harbours in Georgia, on the eastern side of the Black Sea, which provided the main bases for the surviving fleet. It should be noted, though, that these ports, such as Poti, possessed only very limited repair facilities, and this significantly reduced the operational capability of the Soviet fleet.

On 22 June 1941, the Black Sea Fleet comprised the battleship Parizhskaya Kommuna, the cruisers Molotov, Voroshilov, Chervona Ukraina, Krasny Krym, Krasny Kavkaz and Komintern, the destroyer leaders Kharkov, Moskva and Tashkent, 11 modern destroyers (six 'Type 7' and five 'Type 7U'), five old destroyers (four 'Fidonisy' class and one 'Derzky' class), 15 multi-purpose small ships (two 'Uragan' class and 13 'Fugas' class), 44 submarines and 84 motor torpedo boats.

The Romanian naval forces in the Black Sea comprised four destroyers, one torpedo boat, three motor torpedo boats, eight submarines, three minelayers, one submarine tender, three gunboats and one training ship. The destroyers were the Italian-built Mărăști, Mărășești, Regele Ferdinand and Regina Maria. The torpedo boats was Sborul built in Austria-Hungary, and the motor torpedo boats, all built in the UK, were Viscolul, Viforul and Vijelia. The minelayers were Regele Carol I, which was also a seaplane tender, and Amiral Murgescu, which was also an escort. The submarine tender was Constanța. The gunboats were Sublocotenent Ghiculescu, Eugen Stihi and Căpitan Dumitrescu. The training ship was Mircea. The submarines were Delfinul, Rechinul and Marsuinul, together with the midget submarines CB-1, CB-2, CB-3, CB-4 and CB-6.

As Turkey was neutral during World War II, the Axis nations could not transfer warships to the Black Sea via the Bosporus strait as the Montreux Convention, signed only a few years earlier, allowed Turkey to close the straits to all military traffic. Adolf Hitler offered to sell Turkey a few submarines so they could legally gain passage to Black Sea, but Turkey refused. However, several small vessels were transferred from the North Sea via railway, street and canal networks to the Danube river. These included six 'Type IIB' coastal U-boats of the 30^th Unterseebootsflottille, which were disassembled, shipped to Romania along the Danube river, reassembled at the Romanian Galați shipyard late in 1942 and afterward sent to Constanța. The Germans also transported 10 Schnellboote motor torpedo boats and 23 Räumboote minesweepers via the Danube, and built Marinefährprahme (armed barges) and Kriegstransporter (transports) in the captured Nikolayev yards. Some ships were obtained in Romania, Bulgaria and Hungary, and then converted to serve the German cause, such as the S-boat tender Romania, the minelayer Xanten and the anti-submarine trawler UJ-115 Rosita. Additional vessels were built in German or local shipyards, captured from the Soviets, or transferred from the Mediterranean nominally as merchant ships. In total, the German naval forces in the Black Sea mainly amounted to six coastal submarines, 16 S-boats, 23 R-boats, 26 submarine chasers and more than 100 MFP barges. The German Black Sea fleet ultimately operated hundreds of medium and small warships or auxiliaries before its self-destruction immediately before the defection of Bulgaria deprived it of its last Black Sea bases. Very few vessels were able to make good their escape via the Danube.

Despite Bulgaria’s neutral status in the German/Soviet war, the Bulgarian navy was involved in escort duties to protect Axis shipping against Soviet submarines in Bulgarian territorial waters. The small Bulgarian navy comprised mainly four old torpedo boats, three modern German-built motor torpedo boats, four Dutch-built motor torpedo boats, two 'SC-1' class submarine chasers and three anti-submarine motor launches. Late in August 1944, 14 MFP landing barges were transferred to Bulgaria.

At Germany’s request, the Italian navy despatched a small force to the Black Sea. This force included six MAS motor torpedo boats, six (originally four) 'CB' class midget submarines and four torpedo motor boats.

Hungary became independent as a land-locked nation in the aftermath of World War I, but some Hungarian merchant ships were able to reach the Black Sea via the Danube river. Hungarian cargo ships were operated as part of Axis sea transport forces on the Black Sea, and thus participated in the Axis evacuation from Crimea.

The Hrvatska Pomorska Legija (Croat naval legion) was formed in July 1941, and initially comprised some 350 officers and ratings in German uniform, but this eventually swelled to something between 900 and 1,000. The legion’s first commander was Andro Vrkljan, later replaced by Stjepan Rumenović. The Croats' purpose in posting a naval contingent to the Black Sea was to evade the prohibition on an Adriatic navy imposed by the 18 May 1941 Treaties of Rome with Italy. This prohibition effectively limited the Croat navy to a riverine flotilla. Upon its arrival at the Sea of Azov, the Hrvatska Pomorska Legija managed to gather 47 damaged or abandoned fishing vessels, mostly sailing craft, and to man them hired local Russian and Ukrainian sailors, many of them deserters from the Soviet navy. The legion later acquired 12 German submarine hunters and a battery of coastal artillery.

On 26 June 1941 the Soviet forces attacked the Romanian city of Constanța. During this operation, the destroyer leader Moskva was lost to mines while evading fire from Axis coastal batteries and destroyers. The Black Sea Fleet supplied the besieged garrison in Odessa and evacuated 86,000 soldiers and 150,000 civilians at the end of October, but lost the destroyer Frunze and a gunboat to German dive-bomber attack in the process. The Soviet hospital ship Armenia was sunk by German aircraft on 7 November, resulting in more than 5,000 deaths, most of them civilian and patients being evacuated.

The Black Sea Fleet played a valuable part in defeating the initial German assault on Sevastopol. In December, there was an amphibious operation against Kerch which resulted in the recapture of the Kerch peninsula. A naval detachment, including the cruiser Krasny Krym, remained in Sevastopol to provide the army with gunfire support. Soviet submarines also raided Axis shipping on the Romanian and Bulgarian coasts, sinking 29,000 tons of shipping. During autumn of 1941, both sides laid many minefields in the southern part of the Black Sea: Romanian defensive minefields sank at least five Soviet submarines (M-58, S-34, Shch-211, M-34 and M-59) during this period, but during such operations the Axis forces lost the Romanian minelayer Regele Carol I, which succumbed to a mine laid by the Soviet submarine L-4: two of the five Soviet submarines (M-58 and Shch-211) were also sunk later on that same minelayer’s fields, and another submarine was similarly sunk in 1942. In total, up to 15 Soviet submarines were sunk by Romanian defensive minefields. Another Romanian minelayer, Aurora was lost when the ship was attacked by Soviet bombers on 15 July.

Operations in 1942 were dominated by the German siege and capture of Sevastopol. During the winter, Soviet warships including the battleship Parizhskaya Kommuna provided fire support and undertook supply missions near Sevastopol. The Soviets continued supply missions until 27 June: the losses were heavy and included the cruiser Chervonnaya Ukraina, the destroyer leader Tashkent and six modern destroyers.

The cruiser Voroshilov and destroyers tried to intervene without success in the 'Battle of the Kerch Peninsula' in May, and the Soviets could not prevent a German landing across the Kerch strait on the Taman peninsula in September. With the fall of Sevastopol., the remainder of the Black Sea Fleet was evacuated to ports on the Caucasian coast of the Black Sea, but these provided only the most limited of facilities. Soviet submarines were active in the western part of the Black Sea, where they attacked Axis shipping. Here a highly unfortunate incident was the sinking the refugee ship Struma sailing under a Red Cross flag: the International Red Cross and the USSR had both been informed of the ship’s nature before she departed, but the ship was torpedoed while being towed. On 1 October the Soviet submarine M-118 was sunk by the depth-charge attack of the Romanian gunboat Sublocotenent Ghiculescu.

In 1943, the Black Sea Fleet was reduced to the following ships, which all suffering the effects of poor maintenance in their bases' straitened facilities: the battleship Sevastopol, the cruisers Molotov, Voroshilov, Krasny Krim and Krasny Kavkaz, the destroyer leader Kharkov, five modern and three old destroyers, and 29 submarines.

The Romanian naval forces lost the anti-submarine gunboat Remus Lepri in 1941 during trials after she had been converted into a minelayer. The submarine Delfinul started an extensive refit at the end of 1942, and this kept it out of action for the remainder of the war. Despite these losses, the Romanian navy reached its peak strength in 1943. The modern Romanian-built submarines Rechinul and Marsuinul were completed in 1942, and five Italian-built 'CB' class midget submarines were acquired in the autumn of 1943, although only two of these could be made serviceable. Four modified 'M' class minesweepers, armed as anti-submarine frigates, were built in Romania from German materials during the year. Thus, the main operational warships of the Romanian fleet comprised four destroyers (two 'Regele Ferdinand' class and two 'Mărăști' class), the sea-going torpedo boat Sborul, 10 anti-submarine frigates (Amiral Murgescu, four 'Mihail Kogălniceanu' class, one 'Sava' class and the four 'M' class minesweepers), five anti-submarine corvettes (three 'Sublocotenent Ghiculescu' class and two 'Smeul' class) and four submarines (Marsuinul, Rechinul and the two 'CB' class midget submarines).

The year’s naval operations initially consisted of several offensive undertakings by the Soviets including the defence of Malaya Zemlya in Novorossiysk and some coastal bombardments and raids. On 7 July, the Romanian destroyer Mărășești sank the Soviet submarine M-31. As the war was going badly for the Axis on other fronts, the Germans began to evacuate their Kuban bridgehead in September, and this was accomplished successfully. Kharkov and the destroyers Sposobny and Besposchadny were sunk by dive-bombers while raiding Crimea. As a result of this loss, Iosef Stalin insisted on personally authorising the use of any large ships. The 'Kerch-Eltigen Operation' followed in November.

By a time early in 1944, the Soviet surface fleet was practically non-operational as a result of its ships' poor state of repair. Most of the offensive work was carried out by small vessels and the Soviet naval air force. The land situation had significantly deteriorated for the Axis. The area around Odessa was liberated in March, trapping the Axis forces in the Crimea. The last Axis forces near Sevastopol surrendered on 9 May 1944 and a considerable number of men were evacuated. Soviet submarines continued to attack Axis shipping and, unknown to the Soviets, one of the ships attacked was Mefküre transporting Jewish refugees from Europe.

On 20 August 1944, the Soviet air forces carried on a large air raid against the main Axis base in Black Sea. A number of targets were sunk including the German U-9 and the old Romanian torpedo boat Naluca which had been converted into an anti-submarine corvette before the start of the war. U-18 and U-24 were both damaged and were scuttled few days later. The naval war in Black Sea was now almost over, but U-boats remained operational until they had run out of fuel: with a single strike, Soviet aviation had halved the German submarine force, but the effect could have been greater if such an attack had been carried out earlier.