The Second Ostend Raid (officially known as Operation VS) was the later of two failed attempts made during the spring of 1918 by the United Kingdom's Royal Navy to block the channels leading to the Belgian port of Ostend as a part of its conflict with the German Empire during World War I. Due to the significant strategic advantages conferred by the Belgian ports, the Imperial German Navy had used Ostend as a base for the U-boat campaign during the Battle of the Atlantic since 1915.
A successful blockade of these bases would have forced German submarines to operate out of more distant ports, such as Wilhelmshaven, on the German coast. This would expose them for longer to Allied countermeasures and reduce the time they could spend raiding. The ports of Ostend and Zeebrugge (partially blocked in the Zeebrugge Raid three weeks previously) provided sea access via canals for the major inland port of Bruges. Bruges was used as a base for small warships and submarines. As it was 6 mi (5.2 nmi; 9.7 km) inland, it was immune to most naval artillery fire and coastal raids, providing a safe harbour for training and repair.
The First Ostend Raid on 23 April 1918 was largely a failure, the blockships grounded too far from the channels to obstruct them. The second attempt also failed, due to heavy German resistance and British navigational difficulties in poor weather. In anticipation of a raid, the Germans had removed the navigation buoys and without them the British had difficulty finding the narrow channel into the harbour in poor weather. When they did discover the entrance, German resistance proved too strong for the operation to be completed as originally planned: the obsolete cruiser HMS Vindictive was sunk, but only partially blocked the channel.
Despite its failure, the raid was presented in Britain as a courageous and daring gamble that came close to success. Three Victoria Crosses and numerous other gallantry medals were awarded to sailors who participated in the operation. British forces had moderate casualties in the raid, while German losses were minimal.
After the German Army captured much of Belgium following the Battle of the Frontiers in 1914, the Allied forces were left holding a thin strip of coastline to the west of the Yser. The remainder of the Belgian coast came under the occupation of German Marine Divisions, including the important strategic ports of Antwerp and Bruges. A network of canals connected Bruges with the coast at Ostend and Zeebrugge, through which small warships such as destroyers, light cruisers and submarines could travel and find a safe harbour from which to launch raids into the English Channel and along the coasts of southeast England. U-boats could also depart from Bruges at night, cutting a day off the journey to the Western Approaches, more easily avoiding the North Sea Mine Barrage and allowing U-boat captains to gain familiarity with the net and mine defences of the English Channel, through which they had to pass to reach the main battlegrounds of the Atlantic.
In 1915–1916, the German navy had developed Bruges from a small Flanders port into a major naval centre with large concrete bunkers to shelter U-boats, extensive barracks and training facilities for U-boat crews, and similar facilities for other classes of raiding warship. Bruges was therefore a vital asset in the German navy's increasingly desperate struggle to prevent Britain from receiving food and matériel from the rest of the world. The significance of Bruges was not lost on British naval planners and two previous attempts to close the exit at Ostend, the smaller and narrower of the Bruges canals, had ended in failure. On 7 September 1915, four Lord Clive-class monitors of the Dover Patrol had bombarded the dockyard, while German coastal artillery returned fire. Only 14 rounds were fired by the British with the result that only part of the dockyard was set on fire. In a bombardment on 22 September 1917, the lock gates were hit causing the basin to drain at low water.
Two years passed before the next attempt on the Ostend locks. The First Ostend Raid was conducted in tandem with the similar Zeebrugge Raid led by Acting Vice-Admiral Roger Keyes on 23 April 1918; a large scale operation to block the wider canal at Zeebrugge. Both attacks largely failed, but while at Zeebrugge the operation came so close to success that it took several months for the British authorities to realise that it had been unsuccessful, at Ostend the attack had ended catastrophically. Both blockships intended to close off the canal had grounded over half a mile from their intended location and been scuttled by their crews under heavy artillery and long-range small arms fire, which caused severe casualties. Thus while Zeebrugge seemed to be blocked entirely, Ostend was open wide, nullifying any success that might have been achieved at the other port.
As British forces on the southeast coast of Britain regrouped, remanned and repaired following heavy losses at Zeebrugge, Keyes planned a return to Ostend with the intention of blocking the canal and consequently severing Bruges from the sea, closing the harbour and trapping the 18 U-boats and 25 destroyers present for months to come. Volunteers from among the force that had failed in April aided the planning with advice based on their experience on the previous operation. Among these volunteers were Lieutenant-Commander Henry Hardy of HMS Sirius, Commander Alfred Godsal, former captain of HMS Brilliant, and Brilliant's first lieutenant Victor Crutchley. These officers approached Commodore Hubert Lynes and Admiral Roger Keyes with a refined plan for a second attempt to block the port. Other officers came forward to participate and Keyes and Lynes devised an operational plan to attack the canal mouth at Ostend once again.
Two obsolete cruisers—the aged HMS Sappho and the battered veteran of Zeebrugge, HMS Vindictive—were fitted out for the operation by having their non-essential equipment stripped out, their essential equipment reinforced and picked crews selected from volunteers. The ships' forward ballast tanks were filled with concrete to both protect their bows during the attack, and act as a more lasting obstacle once sunk. Vindictive was commanded by Godsal; her six officers and 48 crew were all volunteer veterans of the previous failed attempt by Brilliant. The two sacrificial cruisers were, as with the previous attack, accompanied by four heavy monitors under Keyes' command, eight destroyers under Lynes in HMS Faulknor and five motor launches. Like the blockships, the launches were all crewed by volunteers; mostly veterans of previous operations against the Belgian ports.
The plan was similar to the failed operation of three weeks previously. Weather dependent, under cover of a smoke screen, aerial bombardment and offshore artillery, the blockships would steam directly into the channel, turn sideways and scuttle themselves. Their advance would be covered by artillery fire against German shore positions from the heavy monitors at distance and at closer range by gunfire from the destroyers. This cover was vital because Ostend was protected by a very strong 11 in (280 mm) gun position known as the Tirpitz battery, named for the admiral. Once the operation had been concluded, the motor launches would draw along the seaward side of the blockships, remove the surviving crews and take them to the monitors for passage back to Britain. This operation was to thoroughly block the channel, and—coupled with the blockage at Zeebrugge (which the British authorities believed to be fully closed)—was to prevent use of Bruges by German raiding craft for months to come.
All preparations for the operation were completed by the first week of May and on 9 May the weather was nearly perfect for the attack. The British armada had collected at Dunkirk in Allied-held France and departed port shortly after dark. Two minutes after midnight, the force suffered a setback when Sappho suffered a minor boiler explosion and had to return to Dunkirk, unable to complete the journey. Torpedoes fired from motor launches demolished machine gun posts on the ends of the piers marking the canal, beginning the attack. Ten heavy bombers of the newly formed Royal Air Force then dropped incendiary bombs on German positions, but did not cause significant damage. In spite of the fog, air operations continued as planned under the overall direction of Brigadier-General Charles Lambe. At the same time as the aerial bombardment began, the long range artillery of the Royal Marine Artillery opened fire on Ostend from Allied positions around the Belgian town of Ypres.