Ostend was attacked in conjunction with the neighbouring harbour of Zeebrugge on 23 April in order to block the vital strategic port of Bruges, situated 6 mi (5.2 nmi; 9.7 km) inland and ideally sited to conduct raiding operations on the British coastline and shipping lanes.

Capitalising on the natural advantages of the port, the German Navy constructed extensive training and repair facilities at Bruges, equipped to provide support for several flotillas of destroyers, torpedo boats and U-boats.

By early 1918, the Admiralty was seeking ever more radical solutions to the problems raised by unrestricted submarine warfare, including instructing the "Allied Naval and Marine Forces" department to plan attacks on U-boat bases in Belgium.

The Ostend force arrived off the port shortly before midnight and made final preparations; the monitors took up position offshore and the small craft moved forward to begin laying smoke.

[10] As a long-range artillery duel developed, the cruisers began their advance towards the harbour mouth, searching for the marker buoys which indicated the correct passage through the diverse sandbanks which made navigation difficult along the Belgian coast.

With their volunteer crews suffering heavy casualties, the commanders increased speed despite the poor visibility and continued groping through the narrow channels inshore, searching for the Stroom Bank buoy which directed shipping into the canal.

[9] Passing the navigation marker at speed, the cruiser was suddenly brought to a halt with a juddering lurch, throwing men to the decks and sticking fast in deep mud well outside the harbour mouth.

Artillery and long-range machine gun fire continued to riddle the wrecks and the combined crews were ordered to evacuate as the officers set the scuttling charges which would sink the blockships in their current, useless locations.

[9] As men scrambled down the side of the cruisers into Coastal Motor Boats which would relay them to the Offshore Squadron, destroyers moved closer to Ostend to cover the retreat and the monitors continued their heavy fire.

However, rather than simply remove the buoy, the German commander had ordered it moved 2,400 yd (2,200 m) east of the canal mouth into the centre of a wide expanse of sandbanks, acting as a fatal decoy for any assault force.

The defeat at Ostend did not entirely dampen the exuberant British media and public reaction to Zeebrugge, but in the Admiralty and particularly in the Allied Naval and Marine Forces the failure to completely neutralise Bruges rankled.

[14] A third planned operation was never conducted as it rapidly became clear that the new channel carved at Zeebrugge was enough to allow access for U-boats, thus calling for an even larger double assault, which would stretch the resources of the Allied Naval and Marine Forces too far.