The Russian Republic that succeeded the tsar in March 1917 had inherited an empire's war and almost none of an empire's authority. Eight months later, in October, the Imperial German Navy decided to test how much was left. Operation Albion was the largest German amphibious operation of the war: ten battleships, one battlecruiser, nine light cruisers, fifty destroyers, six submarines, and a landing force aimed at the West Estonian Archipelago — Saaremaa, Hiiumaa, and Muhu — the chain of large flat islands that screened the southern entrance to the Gulf of Finland and the approaches to Petrograd itself. Against this the Russians had two ancient pre-dreadnought battleships left over from the Russo-Japanese War, three cruisers, three gunboats, twenty-one destroyers, and three small British C-class submarines that had reached the Baltic two years earlier by an extraordinary diplomatic and engineering route through neutral Scandinavia.

What made the Russian fleet at Moon Sound so unusual was not just its inferior firepower. The fleet had been transformed from below by the events since February. Sailors had organized themselves into democratic committees that vetoed officer orders, denounced the war, and called repeatedly for an immediate peace. Yet many of the same sailors did not want Petrograd — the heart of the revolution — to fall to the German army. They suspected, with reason, that elements of the provisional government under Alexander Kerensky would happily abandon Petrograd if it meant pacifying the revolution. The radio manifestos they broadcast during the battle attacked their own government as bitterly as they attacked the Germans. "The slandered and maligned fleet will do its duty," one said, "but not at the command of a miserable Russian Bonaparte, ruling by the long-suffering patience of the revolution."

The German fleet appeared off Saaremaa on 12 October 1917, landed troops, and within days had taken the island. By 16 October the smaller Russian squadron — the pre-dreadnought battleships Slava and Grazhdanin, the cruiser Bayan, and assorted destroyers — was bottled up in the shallow Moon Sound strait between Muhu and the Estonian mainland. British submarine commanders Lieutenants Sealy, Satow, and Downie of HMS C 27, C 32, and C 26 took shots at German capital ships in the gulf with mixed success. On the night of 16 October, Sealy fired four torpedoes; two hit. C 32 was spotted and bombed and forced to scuttle later. The main Russian-German exchange came on 17 October as Slava and Grazhdanin tried to fight their way out through the Suur Strait. Slava took multiple heavy hits and could not be saved; her crew scuttled her in the channel as a blockship and most got off alive. The destroyer Grom was sunk. By 19 October the rest of the Russian fleet had broken out into bad weather and minefields and escaped to Lapvik in Finland.

On paper Operation Albion was a German triumph: the islands were seized, the Russian island garrisons destroyed, the coastal batteries captured. The Germans counted 156 dead and another 60 wounded — light casualties for an operation of this scale. But the German fleet paid in ships. Mines did most of the damage: the new battleships Bayern and Grosser Kurfürst were both damaged by mines; Kronprinz ran aground on the way back to Kiel and required months of repairs; the destroyer S 64 hit a mine and went down; seven minesweepers were sunk in the operation; the transport Corsica was mined and grounded; the British submarine torpedo damaged the minesweeper tender Indianola. The Russians lost minor ships and won a surprising propaganda victory: the manifestos broadcast during the battle echoed through the revolutionary press for weeks, casting the sailors as the betrayed defenders of a revolution their own government would not save.

The aftermath ran straight into the largest political revolution of the twentieth century. Leon Trotsky later wrote that Kerensky's provisional government, panicked by the loss of the West Estonian islands, began openly preparing to move the Russian capital from Petrograd to Moscow. The Bolsheviks pounced: the government was abandoning the revolution to imperialism. Public pressure forced the plan to be shelved. Three weeks later, on 7 November 1917 by the Western calendar, the Bolsheviks overthrew the provisional government in the October Revolution. The sailors of the Baltic Fleet — including many of those who had fought at Moon Sound — were among the most radical supporters of the new Bolshevik regime. (Within four years, in 1921, those same Kronstadt sailors would rise against that same Bolshevik government and be crushed for it. The wheel of revolution turns fast.) Saaremaa, Hiiumaa, and Muhu remained under German occupation until November 1918. They are now part of independent Estonia.