1918 Royal Navy blockade of the Belgian port of Zeebrugge during WWI
The Zeebrugge Raid (; ) on 23 April 1918, was an attempt by the Royal Navy to block the Belgian port of Bruges-Zeebrugge. The British intended to sink obsolete ships in the canal entrance, to prevent German vessels from leaving port. The port was used by the Imperial German Navy as a base for U-boats and light shipping, which were a threat to Allied control of the English Channel and southern North Sea. Several attempts to close the Flanders ports by bombardment failed and Operation Hush, a 1917 plan to advance up the coast, proved abortive. As ship losses to U-boats increased, finding a way to close the ports became urgent and the Admiralty became more willing to consider a raid.
An attempt to raid Zeebrugge was made on 2 April 1918 but was cancelled at the last moment, after the wind direction changed and made it impossible to lay a smokescreen to cover the ships. Another attempt was made on 23 April, with a concurrent attack on Ostend. Two of three blockships were scuttled in the narrowest part of the Bruges–Ostend Canal and one of two submarines rammed the viaduct linking the shore and the mole, to trap the German garrison. The blockships were sunk in the wrong place and after a few days the Germans had opened the canal to submarines at high tide. Lessons were learned during the operation that would be put to use in the Second World War.
Background.
Strategic developments.
At the end of 1916 a combined operation against Borkum, Ostend and Zeebrugge had been considered by Admiral Sir Lewis Bayly, commander of the Coast of Ireland Station. The plan was rejected due to the difficulty of supplying a landing force and the vulnerability of such a force to a land counter-attack; subsequent proposals were rejected for the same reasons. A bombardment of the Zeebrugge lock gates under cover of a smoke screen was studied by Vice-Admiral Sir Reginald Bacon, commander of the Dover Patrol and the Admiralty in late 1915 but was also rejected as too risky. In 1916, Commodore Reginald Tyrwhitt proposed an attack to block Zeebrugge, which was rejected. Tyrwhitt suggested a more ambitious operation to capture the mole and the town as a prelude to advancing on Antwerp. Bacon was asked to give his opinion and rejected the plan, as did the Admiralty.
Rear-Admiral Roger Keyes was appointed director of the Plans Division at the Admiralty in October 1917 and on 3 December submitted another plan for the blocking of Zeebrugge and Ostend using old cruisers in a night attack in the period from 14 to 19 March. Bacon also proposed an operation on 18 December, which combined Tyrwhitt's landing on the mole with a blocking operation. A monitor, , was to land 1,000 troops on the mole, the monitor was to bombard the lock gates and fortifications from short range; the blockships were to enter the harbour in the confusion. The raid was proposed in 1917 by Admiral Sir John Jellicoe but was not authorised until Keyes adapted Bacon's plan for a blocking operation, to make it difficult for German ships and submarines to leave the port. The raid was approved in January 1918 and volunteer crews were obtained from the Grand Fleet "to perform a hazardous service".
Tactical developments.
The possibility of a landing on the Belgian coast was not abandoned, despite the number of rejected plans and early in 1917, Bacon assisted in the planning of Operation Hush, landings by the three brigades of the 1st Division around Middelkerke at the northern extremity of the Western Front. The operation was dependent on the advance of the British armies in the Third Battle of Ypres and had no influence on events at Zeebrugge and Ostend. If landings at the ports were successful, the forces involved would be doomed unless they were relieved by the advance of the armies in Flanders. Bacon devised a plan to destroy the lock gates at Zeebrugge by bombardment with the 15-inch guns of the monitors , and .
The bombardment would have to be undertaken at long range, because of the danger of return fire from the battery at Knokke and meant aiming at a target in area at a range of , using directions from an artillery-observation aircraft. Bacon calculated that 252 shells would be necessary and that it would take at least 84 minutes to fire them. If the attempt began with surprise and the bombardment ships were obscured by a smoke screen, the German guns at Knokke might not have enough time accurately to return fire before the bombardment ended. Bacon thought that the destruction of the lock gates was worth the sacrifice of a monitor but that risking all three for no result was impossible to avoid.
The plan needed a rare combination of wind, tide and weather; to obtain surprise the monitors would need to be in position before dawn. Mist and low cloud would make artillery observation from an aircraft impossible and the wind would have to be blowing from a narrow range of bearings or the smoke screen would be carried over the ships and out to sea, exposing them to view from the shore. Such conditions were unlikely to recur for several days, making a bombardment on the following day most unlikely. The bombardment force sailed for Zeebrugge three times but changes in the weather forced a return to England each time. On 11 May, Bacon ordered another attempt for the next day; a buoy was laid to the north-west of the mole as a guide and a second buoy was placed in the bombardment position. A bearing was taken from the buoy to the base of the mole at Zeebrugge by a ship sailing from the buoy to the mole, despite a mist which reduced visibility to a mile and the ship advancing perilously close to German shore batteries. The ship returned to the buoy by 4:45 a.m., with the bearing and distance. The bombardment ships had taken position, the Motor Launches had formed a line, ready to generate the smokescreen and the escorts formed a square around the monitors. Five destroyers zigzagged around the flotilla as a screen against U-boats, the minesweepers began operating around the monitors and the covering force cruised in the distance, ready to intercept a German destroyer sortie.
Zeebrugge, 12 May 1917.
The bombardment opened late because of the need to tow "Marshal Soult", slowing the armada and also by a haze off the harbour. Two Royal Naval Air Service (RNAS) artillery-observation aircraft from Dunkirk, which had taken off at 2:00 a.m., had to wait from 3:00 a.m. over Zeebrugge for almost two hours. The aircraft were met by seven Sopwith Pups from 4 (Naval) Squadron RNAS, which patrolled the coast from 5:45 a.m. as six Sopwith Triplanes of 10 (Naval) Squadron RNAS flew over the fleet. One of the artillery-observation aircraft had engine trouble and force-landed in the Netherlands; the other ran short of petrol. Firing from the monitors was opened just after 5:00 a.m. and at first fell short; many of the shells failed to explode, which left the aircraft unable to signal the fall of shot. The accuracy of the bombardment improved soon after; "Marshal Soult" hit the target with its twelfth shell and "Erebus" with its twenty-sixth. "Terror" was most hampered by the loss of one of the aircraft and by dud shells; only forty-five of the 250 shells fired were reported and the observation aircraft had to return because of fuel shortage at 5:30 a.m., leaving the last half-hour of the bombardment reliant on estimated corrections of aim. Two relieving aircraft also had engine trouble and failed to arrive.
In the first hour of the bombardment, German retaliation was limited to anti-aircraft fire and attempts to jam the wireless of the artillery-observation aircraft. When the Pups from 4 (Naval) Squadron arrived, twice their number of German Albatros fighters engaged them and some of the aircraft from over the fleet, which joined in the dogfight. The British claimed five German aircraft shot down and the fleet was able to complete the bombardment. A third patrol later shot down a German seaplane into Ostend harbour and lost one fighter. At 6:00 a.m. the ships weighed anchor, just as the battery opened fire. Two seaplanes which attempted to approach the fleet were driven off by British fighter seaplanes, which escorted the fleet home. Bacon returned with the impression that the bombardment had succeeded but aerial photographs taken the following week revealed that about fifteen shells had landed within a few yards of the lock gates on the western side and four shells had fallen just as close on the eastern side. The basin north of the locks had been hit and some damage caused to the docks but Zeebrugge remained open to German destroyers and U-boats. The Admiralty concluded that had the monitors been ready to fire as soon as the observer in the artillery-observation aircraft signalled or if the shoot had been reported throughout, the lock gates would have been hit. Bacon made preparations to bombard Ostend harbour.
Ostend, 5 June 1917.
Attempts to bombard Ostend on 26 and 27 May were abandoned because of poor weather but on 4 June, the bombardment ships sailed for the Ratel Bank off Ostend; the bombardment force was smaller and the covering force larger than for the Zeebrugge operation, since surprise was less likely. The Harwich Force provided four light cruisers, a flotilla leader and eight destroyers as a covering force off the Thornton Bank and a second wave of four light cruisers and eight destroyers to guard against an attack from the Schouwen Bank. The firing buoy and its bearing and range from the target were established using the Zeebrugge method and the escorting ships formed a square around the bombardment ships.
German destroyers were sighted east of the Ratel Bank at 1:42 a.m. by and which were steering towards Ostend to establish the range and bearing of the target from the sighting buoy. The German destroyers frustrated two attempts to enter the harbour, which left the fleet without sighting data and reliant on dead reckoning. At about 2:30 a.m., gunfire was heard from the direction of the covering force to the north and at about 3:00 a.m. the bombardment force Motor Launches began to lay a smokescreen. At dawn the coast became visible and Bacon corrected the position by taking a bearing on Sint-Petrus-en-Pauluskerk. The bombardment commenced at 3:20 a.m., German coastal guns replied within minutes and fired accurately at "Erebus" and "Terror" but with no effect.
The British bombardment ceased at 4:00 a.m.; the fleet weighed anchor at 4:20 a.m. and withdrew northwards. The covering force guarded the ships from a point distant, having engaged two German destroyers as they tried to reach Zeebrugge, sinking . Ostend was a larger target than Zeebrugge and could be seen from the sea, which made accurate shooting easier. The dockyard was hit by twenty out of 115 shells and intelligence reports noted the sinking of a lighter, a UC-boat, damage to three destroyers and that the German command had been made anxious about the security of the coast. Had Bacon been able to repeat the shore bombardments at short intervals, naval operations from the Flanders coast by the Germans would have been much more difficult to organise. More bombardments were planned but these were all postponed because essential conditions of tide and weather were not met. After several months, the bombardments resumed but the Germans had been able to repair the damage. As the long methodical bombardments of Ostend and Zeebrugge had proved impractical, Bacon attached a large monitor to the forces which patrolled coastal barrages, ready to exploit opportunities of favourable wind and weather to bombard Zeebrugge and Ostend, which occurred several times but had no effect on the working of the ports.
Prelude.
German defences.
By 1917 the German defences on the Flanders coast included , a heavy artillery battery at Knokke, east of the Bruges Canal, of four guns, with a range of and the battery of four guns, with a range of , west of Ostend. Two more batteries were being built in early 1917 and between the main defences were many mobile guns, entrenchments and machine-gun nests. The only vulnerable