The Germans used mustard gas for the first time, captured part of the bridgehead over the Yser and annihilated two British infantry battalions.

On 26 October 1914 the First Lord, Winston Churchill wrote to Sir John French, commander of the British Expeditionary Force (BEF) "We must have him off the Belgian coast".

[1] Churchill offered naval fire support for an army operation and French adopted the idea for the main effort of 1915.

[2] In early 1916 the idea of a coastal attack was revived and talks began between Sir Douglas Haig the new BEF commander-in-chief and Rear Admiral Reginald Bacon, commander of the Dover Patrol.

[2] Haig appointed Lieutenant-General Aylmer Hunter-Weston, who had commanded the 29th Division and then VIII Corps at Gallipoli, to work with Bacon on the plan.

Bacon proposed to land 9,000 men from six monitors and 100 trawlers in Ostend harbour, with decoys towards Zeebrugge and Middelkirke, as a coastal assault began from Nieuwpoort.

[3] The Battle of the Somme in 1916 forced Haig to postpone an offensive in Flanders until 1917 and the coastal attack depended on retaining the Yser bridgehead, because the river was deep, tidal and 100–200 yd (91–183 m) wide.

HMS General Wolfe and the other monitors would push the pontoons up the beach, the tanks would drive off, pulling sledges full of equipment, climb the sea-walls (an incline of about 30°), surmount a large projecting coping-stone at the top and then haul the rest of their load over the wall.

[7] In experiments on the Thames Estuary, the pontoons performed exceptionally well, riding out very bad weather and being easier to manoeuvre than expected, leading to hopes that they could be used again after the initial assault to land reinforcements.

[10][a] By 10 July the Fourteenth (Army) Wing of IV Brigade had arrived, the brigade taking responsibility for reconnaissance in the area Keyem (now Keiem), Ichtergem, Bruges, Blankenberghe (now Blankenberge), Oost and Dunkirk Bains until 13 July, then Keyem, Oostcamp, Zeebrugge, Oost and Dunkirk Bains, while Royal Naval Air Service (RNAS) units reconnoitred as required.

Reconnaissance flights by IV Brigade RFC and the RNAS aircraft were hampered from 7 to 9 July by ground mist and clouds down to 900 ft (270 m).

[15] A landing operation would begin at dawn under the command of Rear-Admiral Bacon and an army division in three parties of about 4,500 men each, would disembark on the beaches near Middelkirke, covered by a naval bombardment and a smoke screen generated by eighty small vessels.

All the landing forces were to rush inland towards Leffinghe and Slype, occupying bridges over the Plasschendaele canal and road junctions nearby.

[c] Unternehmen Strandfest (Operation Beach Party) a spoiling attack by the reinforced 3rd Marine Division with the 199th Division in reserve, was planned to capture ground east of the Yser, from Lombartzijde creek to the sea, led by the Guard Corps commander General Ferdinand von Quast, who took over Gruppe Nord on 30 June.

[20][d] In June 1917 Krupp completed the construction of Batterie Pommern at Koekelare with Langer Max, the biggest gun of the world, an adaptation of its 38 cm type.

The gun played an important part in the German defence of Flanders and was used to bombard Dunkirk 31 mi (50 km) distant, to stop the unloading of supplies and was sometimes used for diversionary operations.

[22] Unternehmen Strandfest (Operation Beach Party, also the Battle of the Dunes) began with a German artillery bombardment on 6 July, though not of an intensity sufficient to suggest an attack.

[23] German aircraft made low-altitude strafing attacks and by late afternoon, the British troops on the west bank of the Yser were pinned down.

Groups of the specialist Marine Korps Sturmabteilung (assault detachment) made up the first wave and advanced to the third breastwork, overwhelmed the defenders and moved forward to the Yser bank after a short pause.

[25] In twenty minutes German troops reached the river bank and isolated the British parties still resisting, 70–80 per cent having already been killed or wounded by the artillery bombardment, ...the enemy was using a new gas shell freely.

The German advance stopped at the second breastwork, which had been made the objective as the ground behind could be easily flooded; a counter-attack overnight by the garrison and some reinforcements regained the position, except for 500 yd (460 m) near Geleide Brook.

Haig resisted suggestions to launch the operation independently, wanting it to be synchronised with the advance on Roulers, which loomed in early October but did not occur until a year later.

[28] In 1936, J. F. C. Fuller, a former staff officer of the Heavy Branch Machine Gun Corps, called the scheme "a crack-brained one, a kind of mechanical Gallipoli affair".

[29] In 1996, Robin Prior and Trevor Wilson wrote that the amphibious part of the plan was extremely risky, given the slow speed of the monitors and the pontoons having no armour.

[33] The 33rd Division was moved to the coast in August and took over from Nieuwpoort to Lombartsyde, spending three weeks in the line, under night bombing and gas shelling.

[34] To keep British preparations secret, crews from 52 Squadron RFC and the 1st Division were segregated on 16 July, at Le Clipon, a camp enclosed by barbed wire and a story was put about that it was in quarantine.

Next day the Germans retaliated by recapturing the easternmost post and on 26 August, fired fifteen super-heavy shells into Nieuwpoort, demolishing the 19th Brigade headquarters.

[38] Rawlinson favoured an independent operation, which he thought would get as far as Middelkirke, bringing Ostend into artillery-range, which would make the Germans counter-attack, despite the pressure being exerted on them at Ypres.

Haig rejected the proposal and the September operation was postponed, this time for a night landing under a full moon in the first week of October, unless the situation at Ypres changed sooner.

On 23 April 1918, the Dover Patrol conducted the Zeebrugge Raid and sank block ships in the canal entrance to stop U-boats leaving port.