Operation Tanne Ost ("Fir East") was a German operation during World War II to capture the island Suursaari (Swedish: Hogland; Russian: Гогланд, romanized: Gogland) in the Gulf of Finland before it could fall into Soviet hands.

Suursaari was especially important because it worked as a lock in the Finnish Gulf guarding the minefields keeping the Soviet Baltic Fleet in Kronstadt.

[4][5] At midnight, when a pair of Finnish VMV-class patrol boats were preparing to leave to transport a stranded German radio unit, a German minesweeper arrived at the docks on the eastern side of the island and demanded that the island surrender.

[4][6] When the demand was refused the Germans started to land troops which led to Finnish forces opening fire at 00:55 on 15 September 1944.

While the operation was underway 36 Soviet aircraft attacked the German forces destroying at least a landing craft.

This made the Germans withhold the deployment of the force of three destroyers and two large torpedo boats which were being kept at readiness.