The Gulf of Riga is a wide, shallow inlet of the Baltic, partially closed off from the open sea by the long Estonian island of Saaremaa to the north and the Latvian coast to the south. The city of Riga, sitting at its eastern head, was a major Russian port and an obvious objective for any German offensive on the Eastern Front. By the summer of 1915 the Central Powers were pressing east in great strides, the Russians were retreating across Poland, and the German Army wanted to land troops behind the Russian lines on the Latvian coast to help take Riga itself. For that, the German Navy first had to clear the gulf of Russian warships and mine its entrances closed. Vice Admiral Franz von Hipper got the job. Several powerful ships of the High Seas Fleet — battleships, the battlecruisers Moltke and Von der Tann, armored cruisers, and a swarm of smaller craft — were transferred from the North Sea to the Baltic for the operation.

The first try came on 8 August. Two old German pre-dreadnought battleships kept the Russian battleship Slava — a slightly older but still dangerous ship — at bay while minesweepers tried to cut a path through the inner Russian minefields guarding the entrance. The German plan called for the minelayer Deutschland to slip into Suur Strait under cover of the operation and seal it shut with new mines. But mine clearance was painstaking work in a narrow channel, and the August twilight came too soon. Without enough daylight left to mine the strait, the Germans broke off and tried again later. While the main effort hung fire, German armored cruisers detached to shell Russian positions on the Sõrve Peninsula at the southern tip of Saaremaa, and Von der Tann ranged off to bombard Utö island.

On 16 August the Germans came back, this time with everything: dreadnoughts, four light cruisers, and thirty-one torpedo boats forced their way through the defenses and into the gulf itself. The Russian Baltic Fleet was outgunned and knew it. The destroyer Novik, brand new and one of the fastest warships of her time, fought a sharp action with the German destroyers V-99 and V-100 — V-99 was so badly damaged that her crew ran her aground and scuttled her. The Germans pressed eastward toward Pernau (modern Pärnu), where four large flat-bottomed barges loaded with troops attempted a landing on 20 August. Small Russian warships drove them off. A Russian gunboat was sunk in a separate engagement against a German light cruiser and eight destroyers.

Through it all, the German battlecruisers patrolled the open Baltic to cover the operation against Russian ships further out. They were not supposed to need protection from below. The British Royal Navy had quietly slipped a small flotilla of E-class submarines into the Baltic earlier in the war by way of Danish waters; one of these, E1 under Lieutenant-Commander Noel Laurence, found Moltke and put a torpedo into her bow on 19 August. The damage was repairable but humiliating. With the operation already running out of time and fuel, with the gulf still not cleared, with the German Army's wider summer offensive shifting focus elsewhere, Hipper called the whole thing off and withdrew. Riga stayed Russian. The city would not fall to the German Army for another two years, on 1 September 1917, in a different operation entirely.

The Gulf of Riga is today a tranquil shoulder of the Baltic, ringed by the Latvian capital, the Estonian summer islands, and the long sandy beach of Pärnu. From a flight passing along the Estonian coast at cruise altitude, the gulf opens out as a broad pale-blue half-circle, with Saaremaa and Hiiumaa rising as flat green slabs to the west and the Sõrve Peninsula tapering south like a finger pointing toward Latvia. Beneath the surface lies a museum of the Baltic's twentieth-century wars — minefields, sunken destroyers, the wrecks of merchant ships from both world wars. Riga itself, with its Hanseatic spires and Art Nouveau facades, gives little hint that German dreadnoughts once tried, and failed, to force their way to its docks.