From 1915 the Germans held most of Courland Province. At the mouth of the gulf the islands of Ösel, Dagö, and Moon sat between the Irbe Straits to the west and Moon Sound to the east. The Russians had built several fortifications and batteries of coastal artillery on the islands to cover these two narrow passageways. In order to fully control the Gulf of Riga, the Germans had to take Ösel, Dagö, and Moon. The plan for a massive amphibious landing was dubbed Operation Albion (Unternehmen Albion) and would be organized by General Oskar von Hutier, commander of the Eighth Army.
The most heavily defended positions were on the Sworbe Peninsula in the southwest of Ösel. These included artillery batteries at Zerel aimed at the Irbe Straits. Tagga Bay on the northwest coast of Ösel was defended by batteries of 120mm guns at Hundsort and 150mm guns at Ninnast, each on either side of the bay. In the northeast, batteries at Pamerort on Ösel and Toffri on Dagö covered the Soela Sound between Ösel and Dagö. The causeway at Orrisar, which connected Ösel Island and Moon Island, was guarded at both ends by Russian troops. Altogether there was about one division of Russians on Ösel.
Operation Albion was carried out by the German XXIII Reserve Corps. The assault troops were.
the 65th Infantry Brigade of the 42nd Infantry Division, consisting of
a) Infantry Regiment No. 17,
b) Infantry Regiment No. 131,
c) Infantry Regiment No. 138;
Infantry Regiment No. 255;
Bicycle Brigade No 2;
Assault Battalion No 10;
Assault Company No. 18.
The Landing Corps would include about 23,000 men, 5000 horses, 1400 vehicles, 150 machine guns, 54 artillery pieces, 12 mortars, and munitions and provisions for 30 days. Nineteen steamers would bring the assault echelons from their concentration at Libau to Tagga Bay on Ösel’s western shore. Learning from the British disaster at Gallipoli and Russian successes in the Black Sea, the Germans had their transports “assault loaded,” meaning the troops and weapons needed to establish a beachhead were on deck or easily accessible while equipment or supplies to be unloaded later were placed deeper in the ships’ holds.
Eight dreadnoughts plus the light cruiser Emden were assigned to suppress the coast defense artillery; all were brought to their pre-assigned places without incident. The only fire support allotted directly to the landing troops were the torpedo boats’ light guns, since the sophisticated fire support offered by the U.S. Navy during World War II was still more than 25 years in the future. At Ösel the Germans had no procedure by which the troops ashore could request fire from the ships. The big ships would fire according to pre-arranged bombardment plans, while the torpedo-boat gunnery officers would observe the shoreline and fire on targets they determined themselves.
Minesweepers went in 24 hours ahead of the invasion, accompanied by three small steamers carrying 1600 bicycle troops and 150 soldiers and sailors who would land at Pamerort. Bicycle Brigade No. 2, brought in from Flanders, was comprised of 144 officers, 5199 soldiers, 734 horses, 4597 bicycles, 215 wagons, 51 automobiles, 111 trucks, and 32 machine guns. The soldiers landed at Pamerort were signalmen and artillerymen trained in using captured Russian guns, while the sailors were armed with ten heavy machine guns.
The 2nd Torpedo Boat Flotilla, a tender, and two steamers carried the 3600-man assault force of Infantry Regiment Nos. 131 and 138. This was followed by two battleship squadrons, a light-cruiser flotilla to provide security for the 14-ship transport fleet, and then the ammunition ships, cargo carriers, water tenders, two hospital ships, two oilers, and a seaplane tender. Cruisers, destroyers, minesweepers, and zeppelins watched for submarines. Altogether the German fleet numbered 363 vessels.
At dawn the 3600 assault troops would land at Tagga Bay, led by regimental assault companies. They would arrive in torpedo boats, the motor launches of the battleship squadrons, and the steamers. Darkness and the element of surprise would allow the assault force to make its way past the forts at the mouth of the bay. The troop carriers preceded the battleships, which would steam in circles to keep the forts under continuous fire. Once the troop carriers made it past the forts, they were safe from gunfire, as the Russian guns were fixed seaward.
The German torpedo boats would use their 105mm guns to suppress the Russian batteries firing from the woods on either side of the bay. Before the troop carriers landed in Tagga Bay, two assault detachments from Assault Battalion No. 10 would attack the two Russian forts at Hundsort and Ninast, which sat on opposite sides of the bay. Two battalions of Infantry Regiment No. 131 would land at Ranna (Veere) on the west bank, while two battalions of Infantry Regiment No. 138 would take the east bank. The assault units were given the mission of securing the beach and forming a defensible perimeter. Only then would the rest of the troops steam into Tagga Bay and land. Ships would bombard the batteries at the mouth and sides of the bay, as well as the seaplane station at Papensholm. Most of the 42nd Infantry Division would capture Arensburg to prevent the Russians from retreating to the Island of Moon in the northeast; simultaneously Infantry Regiment No. 131 would march from Tagga Bay to the Sworbe Peninsula in the south to take Fort Zerel.
At the Cape of Pamerort the secondary landing of bicycle troops was intended to confuse the Russians and place the troops 18 miles closer to their target, the bridgehead to the causeway at Orrisar. The sailors armed with heavy machine guns would hold the cape, allowing the two battalions of bicycle troops to advance inland. One would ride toward Arensburg and the other toward Orrisar.
Naval feints and bombardments of Dagö Island in the north and Zerel in the south would distract from the main landings in Tagga Bay. After the assault force went ashore, the fleet would enter the Gulf of Riga through the Irbe Straits and use its guns to support the 107th Infantry Division at Arensburg and Infantry Regiment No. 131 on the Sworbe Peninsula. Once the Germans had taken Arensburg, the fleet would use the city as its base of operations, providing support for ground troops assaulting Orrisar and Moon.
The amphibious assaults were rehearsed on the beaches at Libau, while at night the men attended lectures by intelligence officers which included magic-lantern shows that depicted the Russian fortifications. To increase the speed of the invasion, the Pioneer Landing Company (Pionier Landungskompagnie) was transferred in from Romania to serve as stevedores, and Pioneer Battalion No. 9 arrived from the Elbe River to build the floating docks, pontoon bridges, and gangways for unloading cargo.
Airships were active during the preparations for Operation Albion. In addition to reconnaissance missions they also conducted bombing raids. During the night of September 24-25 LZ120 dropped over four tons of bombs on the Zerel battery at about 2:45 A.M., which was followed by LZ113 with 400 pounds of bombs. On the evening of October 1, L30, L37, and LZ120 attacked Salis and Salismunde and their environs, dropping a combined total of nearly nine tons of bombs. Since the area was poorly defended, L30 attacked from only 4000 feet.
The rain and fog were heavy on the morning of October 12, 1917. At around 5:44 A.M. the German fleet opened fire on Ösel. A short time later two launches landed men from Assault Battalion No. 10. The torpedo boats offshore used their guns to support the assault force; the laborious, time-consuming process was to put naval officers ashore who found the units in question and asked them where they wanted the fire. The officers then returned to their ships and identified the visible targets. It could take as long as two hours to complete one fire-support mission.
During the assault German seaplanes launched from a tender performed vital reconnaissance flights. The heaviest fighting took place at Orrisar, where one bicycle battalion and Assault Company No. 18 took the Ösel side of the causeway leading to Moon and the second bicycle battalion covered the road from Arensburg to Orrisar. Naval forces in the Kassar Inlet in the north served as artillery support, bombarding the Russians incessantly. The trapped Russians tried for two days to break through the bicyclist battalion at Orrisar, but surrendered when the 42nd Infantry Division arrived on the scene after a forced march in pouring rain from Arensburg.
By October 16 the battle for Ösel was over; the Germans then launched several assaults across the causeway into Moon. The assault company of Infantry Regiment No. 138 finally succeeded in crossing and taking the fortifications guarding the causeway. The remainder of the regiment joined the assault company and secured Moon by October 17. On October 19 Infantry Regiment No. 17 was ferried across Soela Sound to Dagö Island, where it faced weak resistance. The land battles had ended.
At a tactical level, Operation Albion was an unqualified success. The Germans took the islands and captured 20,130 Russians, 141 cannons, 130 machine guns, 2000 horses, two armored cars, 28 automobiles and trucks, and 10 aircraft. German casualties were three officers and 51 soldiers killed and six officers and 135 soldiers wounded; four naval officers and 152 sailors were killed, and 60 sailors were wounded. Seven small German ships were sunk before and during the operation, and another two that ran aground were later scuttled.