The Blocking of Zeebrugge

by Alfred Francis Blakeney Carpenter

CHAPTER I

THE STRATEGICAL SITUATION. THE GERMAN BASES
IN FLANDERS. THE CONCEPTION OF THE PLAN.

The main function of a navy in war is that of obtaining the command of the sea. The purpose for which such "command" is desired is the utilisation of the sea-lines of communication and the denial of the same to the enemy.

Soon after the commencement of the war in 1914 the sea-lines of communication across the English Channel assumed considerable, if not paramount, importance for the transfer of personnel and material from Britain to the Allied forces in France. It was equally incumbent on the navy to maintain the trans-Atlantic and other lines of communication along which the necessities of life and war were carried to the Allies in all theatres of war.

The Strategical Situation

The first step towards obtaining "command of the sea" is the removal of the obstacles which stand in one's way. In this particular case the main obstacle (admittedly constructed for the purpose) was the German High Seas Fleet. Thus the first duty of the British Grand Fleet was that of destroying the so-called High Seas Fleet, or, if destruction was found to be impracticable, of reducing it to inactivity. The German Fleet was fully alive to that fact, and, almost throughout the war, hid themselves away in their naval bases under the protection of their coast defences. Thus, as events showed, the High Seas Fleet did not prove to be a very serious obstacle to our Command of the sea; but, and this fact is easily forgotten, we could not foresee the continuance of their ineptitude and lack of spirit. The German submarines, however, were a formidable obstacle, indeed. It is unnecessary to reiterate what is already common knowledge on that point.

Submarines, by their nature, have certain limitations. Except in the case of the submarine cruisers, which only materialised in the latter part of the war, such craft are considerably hampered in their movements by their comparatively small radius of action. Owing to the geographical situation of Germany, her submarines were forced to expend an important percentage of their fuel during the outward and homeward voyages between their bases and the trade routes. This expenditure cannot merely be judged by the distances which had to be traversed; the expenditure of fuel in the submarine bears some relation to the whole circumstances of the voyage.

The endurance of the personnel is another important factor, and is similarly affected by the circumstances under which they are employed. For instance, in waters patrolled by enemy vessels, high speed must always be readily available and the strain on the personnel, consequent on the danger of sudden attack from surface craft, aircraft, or other submarines, to say nothing of the presence of mine-fields, is increased. Thus the longer the passage that the German submarines were forced to undertake in comparatively narrow and dangerous waters—such as the North Sea—the less work could they do on our more important trade routes. That statement is closely connected with the subject of this book.

It did not require very much intelligence on the part of the German Admiralty to realise that the possession of bases on the Flanders coast would greatly facilitate their submarine campaign owing to the consequent reduction of the voyages to and from the trans-Atlantic, or Channel, trade routes. Flanders was therefore used, as will be explained later in detail, to provide advanced bases for German submarines.

The coast of Flanders lent itself to other naval uses. In addition to the guerre-de-course tactics of the enemy—i.e., the direct attack on Allied merchant vessels—it was always open to Germany to take their whole main fleet to sea for the purpose of seeking advantageous conditions for bringing a portion of our Grand Fleet to action.

Movements of modern fleets under war conditions necessitate the use of various types of small craft to precede them—e.g., mine-sweepers for clearing channels for the fleet to pass through, destroyers for supporting the mine-sweepers and for driving back the enemy's small craft, light cruisers for scouting purposes, etc. Mine-sweepers and torpedo craft, by virtue of their small size, are unable to keep the sea for long periods. It will therefore be realised that, in the event of the High Seas Fleet putting to sea for operations in southern waters, the Flanders coast provided Germany with an advanced base from which their light craft could operate.

The German torpedo craft based in Flanders, therefore, would be able to serve a double purpose, viz., that already mentioned and that of attacking our patrol craft, our coast and our merchant vessels when opportunity offered. The mine-sweepers could also serve a double purpose in that they were required to sweep channels for the ingress and egress of submarines based in Flanders whilst being suitably placed for sweeping duties in advance of the main fleet. That Flanders was also suitable for aircraft bases is as well known as it is obvious; but it may not be generally understood that such aircraft would also be of special value to the main fleet under the conditions stated above. Thus, to sum up, the occupation of the Flanders coast by the German sea forces would be of treble value—to provide, firstly, a base for the submarines employed on commerce destruction; secondly, a base for the advanced flotillas and aircraft operating in conjunction with the main fleet in the event of the latter coming south; and, thirdly, a base from which to attack our southern coasts or sea-patrols and from which to indulge in air raids against British and French territory.

The foregoing consideration of the possible uses of Flanders to the German Navy shows the inherent value of an advanced base in that locality; the intrinsic value obviously depended upon the existence of suitable harbours for use as bases. Let us now examine the geographical situation.

CHART SHOWING THE RELATIVE POSITIONS OF DOVER, ZEEBRUGGE, HELIGOLAND, AND THE EXITS FROM THE NORTH SEA.

In the latter part of 1917 the Flanders coast, as far westward as Nieuport, was in the possession of the Germans. The northern extremity of the line separating the German and Allied armies was situated approximately on the Yser Canal, which emanates from Nieuport harbour. The latter was dominated by the gun-fire of both armies; its use was, therefore, denied to both. The only other harbours on the coast of Flanders were Ostende, Blankenberghe, and Zeebrugge. These will be described in some detail presently.

The Flanders Coast

The Flanders coast consists mainly of flat country barely elevated above the level of the sea. Sand-hills along the shore act as a barrier between the sea and the land. Parallel to the shore the tidal current runs to and fro with considerable velocity. The tendency for the tidal current to wash away the sand from the shore is partially countered by the use of groynes, such as are similarly used to maintain our own coastline in many parts of England. Although the groynes on the Flanders coast are carried well out into the sea—they are often 100 yards in length—the movement of sand along the coast is very considerable, and, as will be explained later, has a strong influence on the harbour situation in that locality.

The approaches to the coast are beset with shoals reaching to a distance of eight miles from the land. These shoals have always provided serious obstacles to navigation. During times of peace the charts of this locality had been kept corrected by virtue of continual surveying. The shoals were frequently moving and new shoals appeared from time to time. The channels required almost constant dredging. For obvious reasons during the occupation of Flanders by the Germans it was not possible for the Allies to continue either the surveying or the dredging.

Before the war navigation off this coast required the use of many facilities such as buoys and lighthouses. At the best of times buoys are not very dependable as navigational aids owing to their tendency to break away in heavy weather or to drag their anchors along the bottom. Their positions need to be "fixed" from time to time by means of angles to shore objects, or by methods of astronomical observation, and then compared with the positions shown on the charts. Lighthouses, however, unless they are of the small type without lighthouse-keepers, are more efficient aids to the navigator. During the war the lighthouses east of Nieuport were only used by the Germans during short periods when specially required for their own craft; the majority of the buoys were withdrawn and the remainder were moved to new positions which were frequently altered to prevent the Allies from making use of them. Thus, during the war, the charts available to the Allies were very soon obsolete; no others were obtainable. Navigation off the Flanders coast, for Allied vessels of any size, therefore, became decidedly hazardous.

The tides on the coasts, in addition to running alternately eastward and westward with considerable velocity, also caused large differences in sea-level amounting to fifteen feet between the highest and lowest states of the tide.

The Canal System

Mention has already been made that the only harbours on the coast eastward of Nieuport were situated at Ostende, Blankenberghe, and Zeebrugge. But these were not natural harbours. They had been artificially cut out of the coast-line by means of dredging. The entrance channels were preserved by piers built out into the sea and by dredging operations designed to retain the desired depths of water.

BIRD'S-EYE VIEW OF CANALS

Ostende, before the war, had been much used as a commercial harbour, and was therefore provided with numerous wharves, basins, and docks. It was a suitable harbour for all classes of submarines and torpedo craft. Blankenberghe was a little harbour about nine miles east of Ostende and three miles west of Zeebrugge. Its depth was exceedingly small; it could, therefore, only be used for shallow draught vessels such as fishing boats, motor boats, and the like. It was true that the rise of tide, amounting to approximately fifteen feet, would enable larger vessels to enter or leave near the time of high water, but any naval vessel stationed in a harbour from which it can only proceed to sea during a limited portion of the twenty-four hours at once loses much of its value. Zeebrugge could accommodate vessels up to a considerable size: the harbour works and depths will be described in detail presently. Although these three places provided the only harbours on the coast, there was a harbour of great importance at Bruges, about eight miles inland from Zeebrugge.

Bruges harbour was also entirely artificial, consisting of locks, basins, and waterways built on the canal system. Bruges was connected to the sea by means of canals running to Zeebrugge and Ostende, these canals converging on the waterways of Bruges in such a manner that vessels of a certain limited size could pass from Ostende to Zeebrugge, and vice versa, without actually proceeding into the open sea. A series of small canals also connected Bruges to Antwerp, via Ghent, but this canal system, being only constructed to accommodate barges, did not materially add to the value of Bruges as a harbour for sea-going vessels.

Of the three canal systems connecting at Bruges, the canal to Zeebrugge easily held first place in importance. This canal was built by the Belgians. It was commenced in 1896 and completed in 1907. Six and a quarter miles in length, it was almost entirely straight throughout. It could accommodate torpedo-boat destroyers or submarines, both of the largest size, and could, if required, have been used by light cruisers.

The Harbours in Flanders

At the seaward end of the Ostende and Zeebrugge canals, locks were constructed so that vessels could pass from the canals to the sea, or the reverse, at any state of the tide, without lowering the level of the water in the canal.

The above-mentioned harbours were used for naval purposes by Germany as follows. Bruges was chosen as the main naval base. Shelters for protecting submarines from aerial attack, floating docks, repair workshops, all the other facilities which go to make a modern dockyard for small vessels, and the necessary stores and ammunition, were to be found there. The number of naval craft based on Flanders appeared to vary considerably; but, at the beginning of 1918, approximately eighteen submarines and twenty-five destroyers or torpedo-boats would be at Bruges on an average day. The submarines lay in the special shelters which were covered by roofs of reënforced concrete several feet in thickness. Bruges, then, was not only the dockyard but also the resting-place of practically all the German naval craft based on Flanders.

The sea exits from Bruges, as already mentioned, were situated at Ostende and Zeebrugge. There was some doubt, however, whether the Bruges-Ostende canal could be used for the passage of anything larger than very shallow draught vessels such as motor boats or barges. The Ostende canal was known to be narrow, tortuous, and shallow; it had been constructed many years earlier than the Zeebrugge canal.

At Zeebrugge and Ostende a few German craft were usually stationed for duties of an immediate nature such as mine-sweeping, patrolling, and duties connected with the defence of the coast. These harbours were specially useful as taking-off places for vessels which had concentrated in readiness for operations at sea, or as bolt-holes for the same craft when pursued by our patrol vessels. Both harbours were open to bombardment from the sea; that reason, more than any other, probably influenced the Germans to use Bruges for their main base. Ostende, being more open to attack from the sea and air than was Zeebrugge, was the less important harbour of the two.

Blankenberghe harbour, owing to its small size and shallow depth, was used as a base for the German armed motor boats; it is believed that about thirty were stationed there. This harbour, being unconnected with the canal system, was not in direct inland communication with Bruges by water.

In addition to the submarines and torpedo craft already mentioned, the Germans had a large number of trawlers based on the various harbours for mine-sweeping and patrol duties. At Zeebrugge they had their largest seaplane base in Flanders; another seaplane base was situated at Ostende.

In due course Flanders had become a veritable hornet's nest. Let us consider for a few moments to what extent these hornets could trouble us.

Our Lines of Communication

Across the English Channel, and especially in its eastern portion, we had established lines of communication of tremendous importance. It is no exaggeration to state that, every few minutes of the day and night, a vessel, of one sort or another, left the English shore for France with her cargo of personnel, guns, ammunition, food or fuel, etc. Day after day, night after night, for months on end, a constant stream of vessels poured across the Channel in support of the Allied armies or on the return trip to English ports with wounded, men to whom a welcome spell of leave had been granted, empties for refilling, motor transport vehicles for repair, and the like. The wounded were carried in hospital ships; but, as the world knows and can never forget, the Germans ruthlessly torpedoed them whenever the chance offered, regardless of the Geneva Convention, heedless of the damnable inhumanity of the proceeding, seeking only for opportunities for indulging in the frightfulness which formed part of their Kultur.

All these vessels were continually open to attack, not only from submarines but also from the surface craft and aircraft based in Flanders. At any chosen moment, preferably at night or during misty days, these hornets could emanate from Ostende or Zeebrugge on their deadly missions. Further westward our trans-Atlantic lines of communication offered innumerable opportunities for the German submarine commanders to display their brutality against comparatively defenceless merchant vessels, or to attack transports carrying munitions of war and troops from the American Continent. The passage through the English Channel afforded the most direct route for German submarines proceeding to, or returning from, their hunting-grounds.

The mercantile traffic off the southeast coast of England and in the entrance to the Thames was also within easy reach of the German bases in Flanders; so were our seaside resorts, such as Ramsgate and Margate, which provided favourable opportunities for bombardments with resultant casualty lists of innocent women and children.

Dunkerque and Calais on the French coast were the nearest seaport objectives to the Flanders coast; they both experienced frequent aerial attacks and an occasional bombardment from the sea.

As a counter to the German craft in Flanders the British Admiralty had established a force known as the "Dover Patrol." As the name implies, this force was primarily based on Dover. Their duties were mainly those of protecting the transports bound across the English Channel, preventing the German naval craft from passing through the Straits of Dover, and watching the exits from Bruges so as to obtain timely information of concentrated German forces putting to sea. The story of the Dover Patrol is of intense interest, but so many pages would be required to do it even bare justice that I can only refer the reader to books written especially on that subject. Suffice it to say here that, day and night, winter and summer, fair weather and foul, the Dover force patrolled the sea so successfully that the German attempts to use their surface craft for attacking the Allies were few and far between. The difficulties of preventing the submarines passing through the Straits of Dover were immense. We must realise that the maximum portion of a submerged submarine visible above water amounts to a periscope of a few inches in diameter. Compare that dimension to the width of the Strait which at its narrowest part is twenty miles. A few inches in twenty miles—if I have calculated aright that means that the visible portion of the submarine would cover little more than one-millionth part of the surface between Dover and Cape Grisnez. And when we also realise that the periscope would only be raised above water for a few seconds at long intervals we shall begin to understand the difficulty of the problem. Yet, as we know now, the Dover Patrol force, under the direction of Vice-Admiral Sir Roger Keyes, eventually rendered the passage through the Straits to all intents and purposes impossible for a submarine. All honour to the Dover Patrol!

The Dover Patrol

A point which, until recently, unaccountably seemed to have escaped notice was that the work of the Dover Patrol was carried out on behalf of all the Allies and of the United States. It was not a British force acting solely in British interests. Though it is difficult, and perhaps invidious, to apportion the credit for protecting the Allied lines of communication, yet there is no shadow of doubt that the troops from Canada and from the United States of America owed to the Dover Patrol force a tremendous debt of gratitude for their safe passage overseas. Recognition of this fact has since been shown by the erection at New York, and on the French coast, of memorials to the Dover Patrol. When the late war has faded into history, and those of us who took part have long since "gone west," such memorials will remain to bear witness to the splendid sacrifice and unselfish gallantry of those hardy seamen who did their utmost to uphold the honour of civilisation and to destroy the forces working for its overthrow. (This opportunity of acknowledging the success of their extremely arduous efforts, humble and brief though the acknowledgment may be, partially counterbalances my regrets at not having had the chance of serving with the "Dover Patrol" except on the occasion which this book is designed to describe.)

CAPTAIN ALFRED F. B. CARPENTER, V.C., R.N.

The final closing of the Straits, however, was far from accomplished by the spring of 1918. At that time we had reason to believe that a large percentage of the total Allied losses in merchant ships was caused by the Flanders submarines, and that the percentage was on the increase.

Now patrol work of the type described above is essentially defensive in its nature. This statement is not intended to imply that the Dover Patrol force were always employed on defensive tactics; such was by no means the case. Our monitors frequently bombarded the coast defences and the harbour works at Ostende and Zeebrugge; our motor boats were continually patrolling close off the three coast harbours, watching for opportunities to torpedo any German vessels which ventured to sea; our mine-laying craft were employed, night after night, in laying mines to the detriment of the German submarines. But from time to time various suggestions had been made that we should adopt still more offensive measures against the enemy. It is a very simple matter to make suggestions, but by no means so simple to accompany them with a reasoned statement, based on logical deduction, which will convince the authorities of their value. Until a particular Plan has been put into execution it may, in the literal sense, be rightly designated a "paper scheme." It is both unreasonable and unfair to attach a derogatory sense to the term. It is equally unreasonable for authors of schemes which have not passed the paper stage to belittle operations when the latter, based on schemes which differed from their own, have actually taken place with successful results.

Paper Schemes

Whatever suggestions were made, it is clear that there could be only two radical methods of attaining our object. The most satisfactory, of course, would have been the recapture of the Flanders coast and of Bruges, with all the hornets in their nests, by means of military operations. Unfortunately that was impracticable; the Allied armies were not yet sufficiently strong. The only alternative to capture of the craft in their harbours was that of preventing them putting to sea—i.e., destroying or blocking their exits. Several schemes for blocking operations had been proposed. In tactical method they had varied from blowing up the harbour entrances, as suggested by the Halifax disaster, to "building in" the entrances under cover of poison gas. Whether such methods were considered too risky, too expensive, or too hopelessly fantastic is more than the author of this book knows.

An attack on Zeebrugge had been strongly advocated by an eminent flag officer in November, 1916, but no details were given by him as to the nature of the operation. In May, 1917, detailed proposals for an attack had been submitted to the Admiralty by another distinguished officer. This attack involved a landing on the Mole at Zeebrugge, the general idea of which was not dissimilar from that eventually followed. This particular scheme had not earned the approval of Their Lordships, nor was it considered suitable by the Vice-Admiral then in command at Dover.

Many months after the blocking of Zeebrugge had become an accomplished fact two earlier schemes came to light—these having emanated from the author of that submitted in May, 1917. In November, 1917, however, the only previous proposals which were available for consideration by the Planning Division of the Staff were those of November, 1916, and May, 1917, mentioned above.

In November, 1917, Admiral Sir John Jellicoe was First Sea Lord and Chief of the Naval Staff. He had requested the Director of Plans to consider, amongst many other things, the possibility of blocking the Belgian ports.

The Plan was evolved in the Admiralty, being commenced on November 13th, and laid before Their Lordships on December 3d. The Plan was accepted as feasible, and earned Their Lordships' decision to have it carried out. No previous Plan had reached that stage. The original edition of the Plan did not emanate from another country, or from civilian sources, or from any other source outside the Admiralty buildings in Whitehall except in so far as the details of one particular phase of the operation were the outcome of conversations, at the headquarters of the Air Force, with an expert on the formation of artificial fogs.

The Conception of the Plan

The foregoing definite fact has been purposely inserted to correct other statements which have been published elsewhere, presumably in error. I shall deal with the details of the Plan in a subsequent chapter.

Before leaving the consideration of the origin of the Plan, I should like to emphasise one particular point. Perhaps this can be most readily illustrated by a simple simile. An uncorked bottle, containing some noxious fluid, stands upon the table. You realise the disagreeable results which will follow on the escape of its contents. You cork the bottle. Now your action is so obviously correct that you scarcely give it another thought. If any credit was due to anybody you would probably take it to yourself; you would not apportion any particular merit to that fond parent who first initiated you into this obvious solution of the problem. In the case, therefore, of the Blocking of Zeebrugge one need not apportion credit to the person who first suggested the mere idea; the credit is entirely due to the man who, in spite of all the difficulties, evolved a method of "corking the bottle" and who, later, overcoming the great obstacles in the way, carried the method into execution.

Before we pass on to review the difficulties of blocking the exits from the German bases it would be advisable to consider the probable effects of such an operation; this being the logical sequence actually followed before the details of the Plan were formulated.

The results to be attained by blocking the exits would probably be as follows. Firstly, there would be a reduction in the number of Allied vessels sunk by mine or submarine warfare; secondly, a decrease in raid activity on the part of the enemy torpedo craft; thirdly, the loss of a convenient advanced base for small craft operating in conjunction with certain movements of the High Seas Fleet; and, fourthly, the reduction in the number of enemy vessels available for the purposes mentioned.

The first two results concerned reduction of enemy activity arising from the longer passages involved by the use of more distant bases such as Heligoland or the German rivers from which the small craft could continue their depredations. The third result speaks for itself. With regard to the fourth, it has already been stated that, on an average day, there would be many torpedo craft or submarines resting and repairing at Bruges. If the exits were blocked the use of these craft would be denied to the enemy, just as effectually as if they were sunk, for as long as the exits remained unopened. This loss to the enemy, temporary or permanent, could doubtless be described in terms of reduction of Allied losses of merchant tonnage. The Admiralty authorities could probably have calculated, within fairly correct estimates, the average loss of merchant tonnage caused to the Allies by a single enemy submarine or surface torpedo craft. Our former average loss per given period would thus be lessened in proportion to the number of enemy vessels bottled up in the canals during that period.

Results to be Obtained

There would, of course, be other, less important, consequences arising from the blocking of these exits; e.g., the inconveniences caused by the necessary transfer of fuelling and repair facilities elsewhere, the extra work thrown on the escorting vessels in the Bight, and the fact that the craft already at sea and operating from the Flanders coast would be forced to curtail their current trips if they desired to arrive at their new bases with their usual reserves of fuel.

All these material gains to the Allies would be of considerable importance, but the moral effect was not unworthy of consideration. The more audacious an undertaking against an enemy the more intense will be the victor's enthusiasm consequent on success, and the greater the despondency and loss of moral to the vanquished. Attempts to block a hostile port in the face of carefully prepared defence measures may certainly be described as audacious, unless the word "impertinent," which the author is inclined to allocate to this particular event, is deemed to be more truly descriptive. If we endeavour to imagine what our own feelings would be on hearing that enemy vessels had entered one of our strongly defended harbours and blocked the entrance, we shall arrive at some idea as to the probable moral effect produced by such an enterprise. In spite of the almost entire absence of activity on the part of the High Seas Fleet, the Germans had never ceased to sing its praises with all the bombast of which their waning spirit was capable. It was not difficult, therefore, to estimate the dejection and consternation that would spread throughout Germany when the success of our efforts became known. The loss of prestige in the German Navy would be not merely certain but perhaps of vital consequence later on.