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
{36} 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.
[Illustration: A portion of Chart 1406, showing the Dover Strait, the
waters between Dover and Zeebrugge, the shoals, the extent of the
German minefields, the section of fortified coast (shaded), and the
danger zone of the German batteries.]
{37}
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.
[Sidenote: 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. {38} 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.
[Sidenote: 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 {39} 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.
{40}
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 {41}
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_.
[Sidenote: 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 {42} 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 {43} 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 {44} 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 {45} 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 {46} 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, {47} 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 {48} 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 {49} 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.
{50}
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 {51} 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.
[Illustration: Plan of CANAL ENTRANCE CHANNEL]
[Illustration: 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.
{52}
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.
{53}
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?
{54}