The 'Someri Landing Operation' was the general designation of a Soviet combined undertaking to take the island of Someri in the Gulf of Finland during the earlier part of the 'Jatkosota' continuation war (8/10 July 1942).

Starting as a small-scale operation to clear a Finnish observation post from the small island of Someri (now Sommers), this became one of the largest surface ship actions of the Baltic theatre.

During the 'Talvisota' winter war of 1939/40 in which the USSR attempted to seize parts of eastern Finland, the Soviet forces captured several Finnish islands in the eastern part of the Gulf of Finland, which provides access to Leningrad and the naval base on the island of Kronshtadt, and in March 1940 these were ceded to the USSR in accordance with the terms of Moscow Treaty which ended the 'Talvisota', and the Soviets then placed small garrisons on some of ceded islands. When the 'Jatkosota (continuation war) began in June 1941, the islands were generally ignored, but in the autumn of 1941 the Finnish navy attempted to retake Someri, which is a small and rocky island which the Finns wrongly believed the Soviets had abandoned. Coming under fire from the defenders, however, the small Finnish landing force withdrew. Over the next few weeks the Finns shelled and bombed the island several times in hopes of forcing the evacuation of the Soviet garrison and, finally, in December 1941 as Soviet forces evacuated Hanko and several other islands in the Gulf of Finland, the garrison of Someri was pulled back to Moshchny island. Soon after this, Finnish coastal forces occupied Someri island as it was well sited for the observation of Soviet movements in the area.

The Finnish garrison totalled 100 men with two 2.95-in (75-mm) field guns and a few 45-mm anti-tank guns, 20-mm cannon and machine guns. During the battle the garrison was reinforced by another 100 men. The Finnish navy deployed the gunboats Turunmaa, Hämeenmaa and Uusimaa, the minelayers Riilahti and Ruotsinsalmi, six 'VMV' class patrol boats and four motor torpedo boats into the area. Several small minesweepers were also employed to ferry ammunition to the gunboats and reinforcements to the garrison. The Finnish air force supported the naval forces and sortied several flights of Brewster B-239 and Fokker D-XXI fighters as well as Bristol Blenheim and Dornier Do 17 bombers to the area.

Further strength was added by the Germans, who provided two the minesweepers M 18 and M 37, and the elderly minesweeper/tender Nettelbeck to support the Finns. A converted merchant ship, SAT Ost (Schwere Artillerie Träger Ost, or heavy artillery carrier east), was also moved to the area to counter Soviet naval artillery, which was believed to be superior to that of the Finnish and German ships.

The force which the Soviet initially sought to retake the island comprised 256 lightly armed men, who were later reinforced by 57 more men from Moshchny island, supported by a force of about 30 'MO' type patrol craft and 'TKA' type motor torpedo boats. When the initial landing failed to surprise or overpower the Finnish defenders, more naval forces were deployed to the area. These comprised the large minesweepers T-205 and T-207, the' Uragan' class guard ship Burya, the auxiliary gunboat Kama, and more patrol craft and motor torpedo boats. The Soviet air forces made many attacks on Finnish ships and positions on the island with Ilyushin Il-4 (DB-3F) and Petlyakov Pe-2 bombers and Ilyushin Il-2 ground attack aircraft protected by Yakovlev I-153 biplane and Yakovlev Yak-1 and Lavochkin LaGG-3 monoplane fighters.

Shortly after midnight on the night of 8/9 July 1942, Soviet aircraft bombed Someri, causing minor damage, and after this a force of 26 Soviet patrol and motor torpedo boats approached the island. There was heavy firing as the Soviet landing force came ashore. Though considerably outnumbered, the more heavily armed Finns, who were fighting from well-prepared positions, drove off many of the boats and contained the landing force on the eastern half of the island. Alerted by the garrison, a sizeable portion of the Finnish navy, as well as several flights of Finnish warplanes, came to the aid of Someri’s defenders. These were able to clear the Soviets from the area round the island but, as they drove off Soviet motor torpedo boats, repelled attacking Soviet aircraft, and bombarded the Soviet troops who had landed, the Finnish gunboats quickly consumed their ammunition and were forced to depart to load fresh ammunition supplies.

Supported by a newly arrived German minesweeper, the Finns managed to bring reinforcements to the island before 12.00 but, once more, their efforts to drive off repeated Soviet motor torpedo boat and air attacks depleted the gunships' ammunition stocks. Soviet artillery ships started to approach and forced the Finnish ships to depart for resupply, which provided an opening for the Soviet boats to approach and in turn reinforce their landing force. Returning once more, the Finnish gunboats drove the Soviet boats away from the island before the fall of night. On shore, the Soviet landing force was driven into a small pocket on the island’s eastern end, but managed to hold its positions there. During the night Soviet ships undertook a long-range bombardment of the Finnish positions, and a few Soviet boats managed to reach the island under cover of darkness.

On the morning of 9 July most of the naval activity came to an end as the Soviet craft and boats withdrew, though the larger Soviet ships continued shelling the area. The Finnish forces, reinforced by SAT Ost armed with a single 6-in (152-mm) gun, which was a piece of ordnance heavier than any carried by the Soviet vessels, attempted to drive them away and the Soviet vessels withdrew under cover of smoke. This proved to be the final surface action of the naval part of the battle. During the morning the last Soviet pockets of land resistance were cleared from the island. There were several more Soviet air attacks, but no further landing attempts.

The Finns and Germans reported the sinking of more than 16 Soviet patrol craft and motor torpedo boats, and credited the Finnish air force with sinking a Soviet auxiliary gunboat. Soviet reports, on the other hand, claimed that several large vessels (Finnish gunboats or large German minesweepers) had been sunk.

The relatively weak performance of the Finnish gunboats showed how badly outdated they had become in terms of their main armaments, and this prompted the Finnish navy to attempt an upgrade. However, as a result of their age and weak hulls, in combination with the Finns' lack of resources, only Hämeenmaa and Uusimaa had been modified by the time the war ended.

In September 1944, under the terms of the armistice ending the 'Jatkosota', Someri reverted to Soviet sovereignty.