'Salpa' was a German and Finnish naval minelaying operation off the island of Lavansaari (Moshchny in Russian) in the Gulf of Finland (early May 1943).
The island had become part of Finland during the Finnish Civil War (January/May 1918) in which Finland secured its independence from Russia, but on the outbreak of the 'Talvisota' winter war in December 1939 the island’s population, which was the largest of any island in the Gulf of Finland, was evacuated in a matter of just a few hours. The Treaty of Moscow which ended the 'Talvisota' in 1940 allocated the island to the USSR, which kept the island right through the 'Great Patriotic War' despite the fact that Leningrad was almost entirely surrounded and many other islands in the Gulf of Finland were taken by the Finns and Germans.
Vitse Admiral Vladimir F. Tributs, commander of the Baltic Fleet, decided that it was worth considerable sacrifice to maintain a Soviet hold on the islands of Seiskari (Seskar in Russian) and Lavansaari, which proved to be increasingly important bases as the war progressed. The Soviets had a minor naval base and a radar station on Lavansaari, which was used as an advanced naval base. On 18 November 1942 the Finnish motor torpedo boats Syöksy, Vinha and Vihuri, as well as a minelaying boat made a daring assault on the harbour of Lavansaari. Syöksy managed to obtain a single torpedo hit on the old gunboat Krasnoye Znamya, which sank at her moorings. The Soviets salvaged the gunboat on 13 November 1943 and recommissioned her on 17 September 1944.