CHAPTER III
THE OUTLYING OBSTACLES. CONSIDERATIONS OF SALVAGE.
Thus far I have only dealt with the local defences of Zeebrugge. But there were many other obstacles in our way—such as the coast batteries, mines, surface patrol vessels, submarines, aircraft, and the vagaries of the weather in addition to the navigational difficulties mentioned in the first chapter.
The coast-line of Flanders bristled with guns. The section of the coast from three miles west of Ostende to six miles east of Zeebrugge, approximately twenty-one miles in length, was defended by two hundred and twenty-five guns; one hundred and thirty-six of these were of the heavy type, i.e., six-inch and above, up to fifteen-inch guns.
At one period of the war, soon after the Germans first obtained possession of that locality, the coast defences had been few and far between. In those days our ships used to bombard from such short ranges as ten thousand yards. In course of time heavier guns were set up on shore so that our vessels were forced to keep at a more respectful distance. The first bombardments from ten thousand yards had been answered by the establishment of German guns having a range of fifteen thousand yards. When better weapons became available for bombardment from twenty thousand yards the Germans replied with guns firing up to twenty-five thousand yards. And thus the duel continued. Finally, the ranges increased to upwards of forty thousand yards (twenty-three land miles). Monitors were specially constructed for this purpose and their marksmanship was wonderfully accurate. This accuracy is borne out by the fact that scarcely any damage was caused to the residential quarter, although Ostende was bombarded again and again; yet works of military importance, such as docks and railway stations, closely adjoining the residential quarter, were hit time after time.
In a straightforward gunnery duel between a ship and a fort, within the effective range of each, the former stands no chance. In these days, however, such duels savour little of the old-time broadside fighting between ships.
Even the largest and most modern coast guns are of comparatively small avail for defensive purposes unless the attacking ships are visible, or unless the firing can be controlled satisfactorily by such indirect means as the use of aircraft for observational purposes. At night the attackers must be illuminated by star-shell, flares, or searchlights. Under the ordinary fog conditions—i.e., when the whole locality is obscured by fog—aircraft cannot observe the results of firing nor can the attacking forces be illuminated.
Under exceptional fog conditions—i.e., when a fog (natural or artificial) lies between the shore guns and the attacking vessels, the latter being in clear weather—good co-operation between the batteries and aircraft in daylight enables the fire to be directed so accurately as to ensure destruction to vessels which remain in the danger zone.
The only alternative to directed firing is that of barrage firing, such as is used so greatly in modern land warfare. The defence guns can establish a shell barrage, for a limited period, across any zone which the attacking ship is attempting to penetrate en route to her objective. The vessel which steams into an efficient heavy gun barrage from modern guns is unlikely to survive.
German Coast Defences
I afterwards visited one of the large German batteries near Ostende, called the Jakobynessen battery, which mounted fifteen-inch guns and fired projectiles weighing nearly one ton each—seventeen hundredweight to be precise. They were mounted in specially constructed gun-pits amongst the sand-hills close behind the shore, and were so well hidden that they could not be seen from a distance of little more than a single gun's length. The projectiles stood over six feet high and were murderous-looking instruments of warfare. These particular guns, and there were others of a like nature, could probably have ranged up to sixty thousand yards (over thirty-four land miles).
The whole area off this section of the coast, up to about twenty miles to seaward, was included in the danger zone of the coast batteries. No vessel could maintain her position in that area, under ordinary conditions of visibility, for more than a few minutes at the outside limit. The reader may consider, however, that a ship desiring to attack the coast would merely have to approach in foggy weather or under cover of darkness. In foggy weather she would be unable to locate her objective—so that can be ruled out. At night she might conceivably arrive within a few thousand yards without being seen or heard. But immediately she was located by the defences the latter would fire their star-shell and switch on their searchlights. The whole area would thus be illuminated like daylight. The vessel discovered under such conditions would probably be blown to pieces within five minutes.
Thus it is manifest that ships cannot approach a hostile coast, in the face of modern defences, under the ordinary conditions of daylight or darkness, or in fog.
We will now consider the mine problem. The German mine-fields extended to a distance of several miles from the coast. We had reason to know of their presence; from time to time, as reported in the press, our vessels had been blown up.
Mine-fields off one's own coast provide a certain measure of defence. But they are also an embarrassment in that one's own vessels cannot pass through them, when approaching or leaving harbour, unless safe channels are kept clear for the purpose. This applied to the mine-fields under review.
The German Mine-fields
The reader may possibly have jumped to the conclusion that all we had to do was to navigate calmly through the German safe channels. It certainly sounds plausible. As a matter of fact, such an idea borders on the ridiculous. Let us think this matter out carefully. Our forces could not pass through such channels unless they possessed information as to the positions of those channels. But if such information were received, the chances would be long odds on the information having been "made in Germany." Far from such information being correct, therefore, the positions mentioned would probably be those of the most dangerous mine-fields. Nevertheless, suppose we received information which, from the nature of its source and data, we had every reason to credit; and suppose we acted on such information. Well, on the voyage across the sea, or even before we actually start, the enemy discover that we intend to attack. What will they do? Their argument would be as follows: "The British are coming over to attack us; they may have discovered the positions of our safe channels; we dare not take any chances so we will mine our own safe channels immediately." Mine-layers, kept ready for instant use, would be sent to sea at once. In a very short space of time, probably an hour would be more than sufficient, the previous safe channels would have been converted into areas of the greatest danger.
There are alternative methods which the attackers may adopt. Firstly, they may advance to the attack preceded by a force of mine-sweepers. Now mine-sweeping is a very slow process if it is to be carried out thoroughly. It is inconceivable that a large force of these vessels could steam about, mine-sweeping, near the enemy's coast for a considerable period without being discovered. Their discovery would give the whole show away; the enemy would know that we were approaching; the whole element of surprise would be lost.
The other method open to the attackers is that of proceeding to their objective without mine-sweepers, after having carefully weighed the probabilities of danger existing on the various alternative routes, and, on arriving at the danger area, passing through it and chancing the result. And that is what we did—we chanced it! But I am anticipating once more.
Outside the German mine-fields, and in any inshore areas which were unmined, German patrol craft would probably be stationed. Patrol craft, in comparatively narrow waters, are effective for discovering the approach of surface vessels in clear weather by day or night. The minimum harm that they could do to the attacking force would be that of reporting the latter's approach. A single alarm rocket might be sufficient. It is, therefore, almost inconceivable that the patrol vessels could be passed without the alarm being given. Any gun-firing would, of course, act as an alarm; ramming, a much more silent method, would be the best course open to the attacking craft if they encountered the patrols.
There were two other forms of patrol, however, which could provide even more serious obstacles.
Submarines, stationed on the route between the attacker's base and the objective, could patrol at periscope depth. The passing of the squadrons, viewed through the periscope of the unseen submarine would be reported by wireless telegraphy immediately the submarine could come to the surface. Thus, long before the attack commenced, the defenders would be perfectly well aware of the attacker's approach, whereas the latter would imagine that their mission was unsuspected. This use of a submarine, as a lookout, would be of infinitely greater importance, in such an event as this, than her use as a torpedo vessel.
Aircraft patrolling off the coast—say at a height of five thousand feet—would be able to see as far as the southeast coast of England, provided the atmosphere were clear. Under average conditions of visibility there would be no difficulty in discovering a naval force several miles distant. Such discovery would be immediately reported to the defences with the same result as that just described in the case of the submarine. The Germans had a strong force of seaplanes based on the Flanders coast. These machines were generally patrolling the vicinity—provided the Allied aircraft were not about.
Summary of Obstacles
We have now arrived at the stage where we can make a summary of the main obstacles in the way of a blocking enterprise at Zeebrugge. There were (a) the aerial patrol; (b) outlying submarines; (c) surface patrol vessels; (d) mines; (e) uncharted shoals; (f) lack of navigational aids; (g) coast defence batteries and illuminating apparatus; (h) the guns on the Mole; (i) the obstruction booms; (j) the harbour defence craft; (k) the shore batteries defending the canal; (l) the difficulties of seamanship in a tideway; and lastly (m) the vagaries of the weather.
In connection with a blocking enterprise at Ostende the same obstacles applied with the exception of those resulting from the presence of the Mole.
The list is undoubtedly formidable though not yet complete. The operation, on the face of it, did not seem to be altogether simple.
In writing this book I may be taken to task for concentrating on the operation at Zeebrugge and leaving the Ostende stories untold.
The latter operations, there were two, would necessitate a volume to themselves. And—this is the all-important point—I am not competent to render a first-hand account of them because I was not in the position of an eye-witness. Let us hope that the story will be written some day, so that the splendid work of poor Godsal,[[1]] who afterwards lost his life at Ostende in my old ship, and of his gallant troop may be properly recorded.
[[1]] Commander A. E. Godsal.
Owing to the fact that we were uncertain as to the extent to which Ostende could be utilised as an exit from Bruges, we naturally decided to assume its efficiency; i.e., to assume that blocking the craft in at Bruges would necessitate blocking both Zeebrugge and Ostende.
The harbour entrance at Ostende was somewhat similar to the canal entrance at Zeebrugge. There were two piers flanking the entrance channel, the whole area being commanded by shore batteries. The only other comparison between the places which calls for mention here is as follows. Whereas the Mole at Zeebrugge provided additional obstacles against entry, it also acted as a landmark from which the canal entrance could be found. At Ostende the defence obstacles would be less complicated, but the harbour entrance would be more difficult to locate.
Now, the decision to block both exits naturally led to the conclusion that they should be blocked simultaneously if practicable. Otherwise the operation at one place would serve as a warning to the other. For instance, it would have been rather absurd for us to block Zeebrugge one night with a view to coming along on the following night to block Ostende. The absurdity would have been only slightly less in degree if we blocked one exit at—say—midnight with the idea of blocking the other at 2 A.M. For the defence batteries at the two places would naturally be in telephonic communication, and even half an hour's notice at the second exit would be sufficient to prepare a very warm reception for us. Simultaneous blocking was our aim; thus the whole operation was directed to that end, a fact which influenced the events to be related.
It has been suggested that "blocking the exit" was not the best method of preventing the egress of German vessels from the Zeebrugge canal. An alternative method, that of destroying the lock-gate by gun-fire, was referred to. The idea sounds plausible enough at first. As a matter of fact, many attempts had been made, by means of long-range bombardments, to achieve that end. They had all failed. The lock-gate appeared to have a charmed life. Huge shell had burst in its vicinity and yet it still remained intact. The suggestion was then put forward that the lock-gate should be bombarded from close range under cover of smoke or gas. This suggestion was accompanied by the opinion that an attempt at blocking the channel would be futile. I am much puzzled at this idea of close bombardment. For it was as obvious, as it was known to be a fact, that the Germans would withdraw the gate into its armoured recess immediately a bombardment was suspected. This would have been the work of a few moments; the outer lock-gate would have been rendered absolutely immune from destruction.
The argument that there were two lock-gates, outer and inner, and that the Germans could not withdraw both, owing to the fear of the canal running dry, also sounds plausible until it is closely examined. Firstly, however, it is clear that the canal would only run dry if both lock-gates were opened at low tide; secondly, an inshore operation at low tide would preclude the use of any craft other than those of shallow draught; thirdly, owing to the presence of the outer wall of the Mole, whose height would be over forty feet at low tide, the bombarding vessels could only obtain a direct line of fire at the lock from a position inside the Mole where the extensive shoals would allow very little room for manoeuvring, to say nothing of the defences on the Mole itself; fourthly, the canal, even if emptied, would refill from the rising tide within a few hours, and there was no certainty that the temporary evacuation of the water would cause serious damage; and lastly, one may assume, if there was really any substance in the idea, that the Vice-Admiral whose many long-range bombardments had failed to achieve their purpose would have long since attempted a short-range attack.
So, the decision to block the entrance at Zeebrugge having been reached, the best position for blocking had to be considered. It has already been shown that the narrowest portion of the channel to seaward of the lock was situated near the shore ends of the wooden piers. Another position even narrower in size was that of the lock-gateway itself. But the mere width of the position chosen was by no means the only consideration.
The actual sinking of the blockships in position did not provide the final argument; a point of great importance concerned the practicability of removing them out of the channel; it is of little use to block a channel in such a manner that it can easily be unblocked. This matter concerns the art of salvage.
Salvage is a highly technical subject, but a few remarks at this stage are necessary if the reader is to appreciate the extent to which considerations of salvage affected the problem under discussion.
Salvage operations must vary according to the circumstances of each particular case. The size of the vessel, the damage which she has sustained, the manner in which she is resting on the bottom of the sea, the nature of the ground, the tides, the depth of water, the degree of exposure to rough seas, the proximity of shelter for salvage craft, and the distance from the land are all factors of importance, but they by no means exhaust the list.
One of our main purposes in considering salvage operations was that of ascertaining the chief obstacles to salvage, so that we could provide the enemy with as many of those identical obstacles as lay in our power.
Another important object, concerning the immediate problem at Zeebrugge, was that of deciding the best type and size of vessel to be used in addition to the question of what particular damage each vessel should receive, and how she should be fitted to defy attempts at removal.
There are three principal methods of removing a sunken ship. First, bodily removal with the aid of some lifting agent. Second, dispersion by explosive means. Third, piecemeal removal by cutting away.
Regarding the first-mentioned method, a small vessel can be lifted by passing hawsers beneath her and securing the ends to salvage craft on the surface overhead. The hawsers being hauled taut at low tide, the vessel will lift off the bottom when the rise of tide lifts the salvage craft, and can then be transported bodily elsewhere. Larger vessels can be lifted by the use of compressed air, or by pumping out the vessel after closing all holes under water. Provided the ship is upright the compressed air method can leave out of account the damage sustained below the vessel's normal waterline, but the remainder of the hull must be rendered airtight. Air can then be pumped into the hull until the vessel is lifted, and she can be towed away as required.
This method has been used successfully when removing large vessels, but the practicability of rendering them airtight chiefly depends on the damage which they have sustained. The pumping-out method, comparatively speaking, is the most simple one to adopt, provided that the damage to the hull is small. The damaged portion must be repaired by divers unless the more elaborate method of building a coffer-dam—i.e., a sort of dock—around the ship, is pursued. Divers cannot work in a strong tidal current or in rough weather. The repair of holes under water is rendered extremely difficult, if not actually impossible, when the bottom of the ship is badly holed with the ship resting on the damaged portion. The ship must be made watertight, or nearly so, below the surface of the sea before she can be lifted. The word "watertight" is qualified here because, as a matter of accuracy, the ship can be pumped out and lifted, provided that the pumps can eject water at a greater rate than the latter is flowing in. Before passing on to consider the next method it may be as well to remark that special difficulty is experienced when moving sand—i.e., silt—has access to the holes in the ship.
Dispersion by means of explosive charges may, under certain circumstances, be a simple operation, but, on the other hand, there are certain conditions which put this method outside the pale of choice. For instance, in the case of a ship sunk in a narrow channel where much silt is experienced, the explosive method is almost worse than useless. For every explosion in a given section of a vessel will tend to shatter that portion into several pieces. Each piece falls to the bottom and forms a new obstruction. Silt then enormously aggravates the situation, for the sand will collect against the obstruction until it becomes a miniature sandbank. Such shoals are then difficult to remove. A bucket-dredger—i.e., a vessel fitted with an endless chain of buckets for scooping up the bottom—will break her buckets as soon as they encounter the steel kernel of the shoal. On the other hand, a suction dredger—i.e., a vessel designed to suck up sand off the sea-bottom—cannot raise solid material. Neither type of dredger can remove the cause of the shoal; any removal of sand under such conditions is merely temporary; the sand will recommence building up the shoal as soon as the dredger ceases work. Dredging against such obstacles is of little more use than dredging against rocks.
There remains the third method, namely, piece-meal removal by means of "cutting away." Cutting away can be accomplished, in the ordinary course of events, by means of acetylene gas cutters or by pneumatic tools. Acetylene gas will cut through steel with little more effort than a knife cutting through india-rubber. But acetylene gas cannot be used under water and cannot cut through large thicknesses of cement. Pneumatic tools provide a very laborious and tedious means of cutting large quantities of steel. Work under water entails the use of divers. Thus, the removal of a ship by the piecemeal process is an exceedingly prolonged undertaking, especially as each piece must be lifted out when cut away; for reasons already stated the pieces must on no account be allowed to fall to the sea-bottom.
From the foregoing remarks we arrive at the following conclusions. The blockships should be too large to lift off the bottom by the hawser method. They should be extensively damaged and sunk in such a manner that they would rest on the damaged portion of the hull. They should be fitted to counter "cutting away" tactics, and should be sunk in positions where silt would render impracticable the explosive method of dispersion; the damage should be so situated as to give the silting sand access to the hull through the holes in the latter.
These general anti-salvage considerations, however, did not furnish us with all the data required. They required to be dealt with in greater detail, and the matter of dimensions was another important factor.
It was essential to render impossible the passage of the German naval craft out of the canal over the top of the sunken blockships. The tide at Zeebrugge rises fifteen feet between its low and high levels. Allowing six feet as the minimum depth required to float small naval craft, it will be seen that the upper portion of each blockship should reach to within six feet of high tide level, or, at least, nine feet above low tide level, when resting on the bottom. The height of the blockship's hull, therefore, would need to be equal to the depth of the sea at low tide level plus, at least, nine feet. Now, the choice of vessel is naturally limited. In the midst of war it is unlikely that a navy would possess many craft, if any, which were not already in use for other purposes. Thus, the dimensions just referred to would have to fall within certain limits, namely, those corresponding to the dimensions of the only vessels from which one is likely to be able to choose. That part of the total height due to the rise of tide was beyond control; it would be the same anywhere in the same locality. Thus, the position chosen for the blocking must necessarily have a low tide depth of such an amount as would make the total depth at high water correspond to the total height of the available hulls.
Then again the number of ships required would depend on the relation between their horizontal dimensions and the breadth of the channel to be blocked. For instance, a single vessel whose beam dimensions were approximately equal to the breadth of the lock gateway would be sufficient to block the latter, provided that the height of her hull also agreed with the conditions just mentioned above.
Now, it had to be borne in mind that if a vessel was sunk in the lock gateway the "cutting-away" method would be greatly facilitated by the erection of cranes and machinery, within a few feet of the vessel, on dry land. This position, being so far removed from the tidal current which runs parallel with the Belgian coast, was unaffected by silt. Thus, although the lock gateway, by reason of its small breadth, could be completely blocked by any suitable vessel sunk therein, the work of salvage would be very much less difficult here than elsewhere.
Further out, between the wooden piers at the canal entrance, the navigable channel was approximately one hundred and twenty feet in breadth; i.e., slightly over one-third of the whole distance between the piers. A vessel of one hundred and twenty feet in length, therefore, would require to be turned dead across the navigable channel before sinking if she was to block every inch of it. Obviously, a vessel of three hundred feet in length would not require to turn herself to anything like the same extent. The maximum depth in this position was believed to be about thirty-six feet at high tide level. Thus, we arrive at the conclusion that a blockship sunk between the wooden piers would need to have a hull whose height was not less than thirty feet, and to have a length of at least one hundred and twenty feet.
Plan of CANAL ENTRANCE CHANNEL
SECTIONAL SKETCH of SUNKEN BLOCKSHIPS
In this position the silt was known to be very active. That fact, taken in conjunction with the exposure to rough seas, the presence of the tidal current, and the impracticability of erecting salvage plant on the land within easy reach of the vessel, rendered it obvious that, all things considered, the position between the wooden piers would be the ideal blocking position if suitable vessels were available for the purpose, and if such vessels were damaged and sunk with due regard to anti-salvage considerations.
It is common knowledge that when vessels are fitted out as blockships they usually carry a goodly cargo of cement. The general notion, however, about the use of this material is that it is merely intended to make the ships heavier and thus less capable of being lifted. That is only partially correct. There is another and more important use for cement, namely, as a counter against the use of acetylene gas for cutting the ships to pieces. The general scheme is that of placing the cement in just those positions where cutting would be most necessary; in our case, in those portions of the ship which would be above the lowest level of the tide and up to within six feet of the highest tide level. The depth of our chosen position being twenty-one feet at low water and thirty-six feet at high water, this meant that the cement would need to be placed between the levels of twenty-one feet and thirty feet above the keel, provided that the ship was sunk in an upright position. With regard to the latter proviso, steps must be taken to guard against the eventuality of the ship resting on her beam ends on the sea-bottom as a result of capsizing when foundering. This cautionary measure necessitated placing the cement between the levels of twenty-one feet and thirty feet from her beam ends at either side of the vessel as well as between the same vertical distances from her keel. Nothing should be left to chance that can be provided for in advance.
It was clear enough that the task of ever getting the ships into the desired positions for sinking would be far from simple; having attained that object it would be the height of stupidity to sink the ships in such a manner, and so fitted, that their removal would be comparatively easy.
After the operation had been successfully completed I could not help being rather amused at a certain individual who expressed the opinion that "the Germans are so cute that they'll probably remove the blockships in a day or two." Why were some people always so ready to credit the Germans with everything that's wonderful? The reasons were not far to seek; such ideas arose partly from natural ignorance on technical matters and partly because the Germans never ceased to assure us how marvellous a nation they were. And some of us believed it! Verb. sap.
With all the difficulties in the way of attainment, what counter considerations were there to make the attempt worth the undertaking?