Read Ebook: The Blocking of Zeebrugge by Carpenter Alfred Francis Blakeney

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So much for the Mole itself. Across the channel the Germans had placed booms. One of these, consisting of four Rhine barges, was moored between the eastern end of the broad part of the Mole and a buoy situated two hundred and seventy yards to the southward. These barges were filled with stone, had nets slung beneath them, and were connected together by wire hawsers. If a surface vessel attempted to pass between the buoy and the Mole she would be brought up by this boom and probably damaged by collision with one of the barges. If a submarine attempted to dive underneath the barges she would be caught up in the nets. The other boom consisted of entanglement nets moored between a series of buoys to the southeastward of the barges. Any ship attempting to pass through them would probably have her propellers entangled, with the result that her engines would be brought to a complete stop. Thus, whichever boom was encountered by a ship, the latter would, at the least, be partially disabled and stopped. The Mole batteries could then have sunk her at their leisure by gunfire. The only route by which a vessel could pass clear of these two booms was that between the southeastern barge and the northern entanglement net; i.e., within two hundred and fifty yards of the heavy gun battery on the Mole. But even if, by dint of good fortune or special good management, a vessel managed to pass the Mole batteries and the booms, she would still have to run the gantlet of the naval vessels in the anchorage and the batteries on shore before reaching the canal.

The foregoing description of the local defences at Zeebrugge has probably been sufficiently detailed to lead to the conclusion that the Germans were fully alive to the possibility of attacks on the Mole or canal. Whether or not they considered that such attacks would only form part of some more ambitious operation, such as a military landing on the coast, our enemies had left practically no stone unturned to repel them. The defence measures must have appeared, especially to those on the spot, to be more than sufficient.

It is well known that, although the possession of detailed local knowledge will usually be of great value towards the formation of plans of attack, there are occasions when local knowledge is apt to make local difficulties loom extremely large. For instance, in this particular case, the navigational difficulties caused by the strong tidal stream, the difficulty of recognising objects on the low-lying shore during darkness, the uninviting appearance of the outer Mole wall as an obstacle to be surmounted, and many other matters would probably have induced the belief, in those who were actually acquainted with these difficulties, that such attacks would have no chance of success. There is, therefore, reason to believe that, although they realised an attack might be attempted, the Germans were perfectly satisfied that the defences could neither be improved nor penetrated.

The reader will probably have arrived at the conclusion that the Germans were devilish in their thoroughness. Yet there was still one joint left in their armour--and we penetrated it. But I must not anticipate.

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 . 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 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.

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 .

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 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.

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.

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 the aerial patrol; outlying submarines; surface patrol vessels; mines; uncharted shoals; lack of navigational aids; coast defence batteries and illuminating apparatus; the guns on the Mole; the obstruction booms; the harbour defence craft; the shore batteries defending the canal; the difficulties of seamanship in a tideway; and lastly 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.

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, who afterwards lost his life at Ostende in my old ship, and of his gallant troop may be properly recorded.

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.

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.

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.

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.

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.

With all the difficulties in the way of attainment, what counter considerations were there to make the attempt worth the undertaking?

PAST EXPERIENCE. SMOKE SCREENS. THE CHANCES OF SUCCESS.

What were the chances of success?

The lessons of personal experience and of past history are the chief guides when calculating the probability of success in any operation. He who ignores history acts unwisely. He who studies history and proposes to attempt something which has always failed hitherto either may be excessively foolish or may be aware of a new factor affecting the situation. He may be merely flying in the face of Providence or basing new proposals on a well-considered judgment of the new circumstances.

In none of these cases were the conditions quite parallel to those at Zeebrugge and Ostende, but some features of each bore a certain similarity.

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