THE MYSTERIES OF SUBMARINE HUNTING EXPLAINED
WHEN all is said and done, anti-submarine warfare is very like big-game
hunting. Success depends entirely on the initiative, skill and resource
of the individual hunter. Contrary to general belief, there is, at
present, no sovereign remedy for the depredations of under-water craft
with their torpedoes and mines. There are, however, several recognised
methods of attack and defence employed by surface ships in this newest
form of naval warfare.
When the new navy took the seas in 1914-1915, bases were established not
only round the coasts of the British Isles, but also in the more distant
seas. The principal danger zones were, however, the North Sea, the
English Channel, the Irish Sea, the Mediterranean and the eastern
portion of the North Atlantic. It was through these waters that every
hostile submarine must pass on its voyage out and home.
This geographical factor restricted the theatre of major operations to
some 180,000 square miles of sea. Minor offensive measures might have to
be adopted against individual U-boats cruising at long distances from
their bases, as actually occurred off the United States coast, but the
fact of Germany possessing large submarine bases only along her own
North Sea coast, and temporary ones on the Flanders littoral, enabled a
concentration of Allied anti-submarine craft to be made in the narrow
seas which afforded the only means of entry and exit to and from those
bases.
The same may be said of Austria in the Adriatic and of Turkey behind the
Dardanelles.
This favourable combination of circumstances would not occur if (however
unthinkable) England, France or the United States were ever to wage a
rigorous war against shipping. The large number of oversea naval bases
possessed by these Powers would cause every sea to become a danger zone
within a few hours of the commencement of hostilities. No effective
concentration of hostile surface craft would be possible with the zone
of operations spread over the water surface of the entire globe, and if
the bases themselves were secured by predominant battle fleets, or
numbers of heavily armed monitors, the seas would quickly become
impossible for purposes of hostile transport.
This geographical restriction of the German and Austrian danger zones
made effective concentration of the Allied anti-submarine fleets and
their devices possible. The 180,000 square miles of sea, forming the
theatre of major operations, was, on special charts, divided into areas,
comprising a few hundred square miles of sea. Each area was given a
distinctive number, and a base was established for its own patrol and
minesweeping fleet.
The areas themselves were again subdivided on special charts into
squares or sections. Each square covered a few leagues of sea and was
known by an alphabetical sign. In this way the waters of the submarine
danger zone were divided into areas, with their bases and protective
fleets, and squares with their respective squadrons or ships.
[Illustration: FIG. 20.--Diagram showing division of sea into
anti-submarine patrol areas.]
Each square of sea was covered once or twice daily by its own patrol
ship or flotilla. Where the danger was less the patrol was not so
frequent and the squares were almost indefinite in size, but where the
chances of successful operations were exceptional, as in the Straits of
Dover, additional offensive measures were employed (see under _Mine
Barrages_).
This, then, was the chess-board on which the game of submarine warfare
was played. To facilitate communication between the different patrols
spread over the squares of sea, wireless was fitted in many ships, and
war signal stations were erected on prominent points of land. Each base
was able to communicate by wireless with any of its ships out on patrol
duty, and was also connected by land-line telegraph, telephone and
wireless with _naval centres_.
These latter were head intelligence offices, usually situated at the
great bases of the battle fleets. In this way any concentration of
hostile surface warships noticed by the patrols (sometimes submarines
were employed, especially in the Heligoland Bight) could be communicated
in a few minutes to the admirals commanding the Grand Fleet, the Battle
Cruiser Squadron or other large fighting organisations.
At the naval centres the movements of hostile submarines were recorded
on charts. If, for example, it was reported from a patrol boat that the
U16 had torpedoed a ship in square "C," area 41, at 10 A.M. (G.M.T.[6])
on 4th August, and the patrol had arrived on the scene too late to be of
any service, a warning could be wirelessed to hundreds of vessels on the
seas surrounding the scene of outrage to keep a careful look-out for
the U16.
[Illustration: FIG. 21.--Diagram showing how an area is covered by
patrols. _A_. Unit or flotilla of ships may proceed out from the base on
course indicated by arrows _B_, which would be called the "Northern
Inner Beat," and return to harbour on course _A_, "Northern Outer Beat."
Other units of ships would simultaneously follow the course _E_. These
and adjacent squares of sea would be covered daily by one or more ships
of each unit. The southern half of the area would be patrolled in the
same way. The "Outer Beat" is shown by the arrows _C_, and the "Inner
Beat" by the arrows _D_. The points _+F_ show the possible positions of
armed patrols acting independently of any unit or flotilla.]
Subsequently a further message might come to the naval centre that the
same submarine had been chasing a merchantman in square "D," "E" or "F"
in the adjoining area. A concentration of fast ships, such as
destroyers, M.L.'s or coastal motor boats, could then be made so as to
intercept the raider or enclose her in a circle while other vessels
hunted her down.
In a like manner important convoys coming down the coast, or entering a
danger zone from the open sea, could be met by a local flotilla and
escorted to a _rendezvous_ with a flotilla from the adjoining area. In
this way they were passed through the submarine and mine infested seas
to and from their harbour terminus.
Almost the same methods were employed in dealing with the thousands of
German mines. But to describe that part of anti-submarine warfare here
would be to encroach on the subject of a succeeding chapter.
PATROLS
The _method_ of patrolling the areas and squares of sea was
comparatively simple, though the same cannot be said of the actual work.
The lines of patrol were called "beats," and there was usually an
"inner" and an "outer" beat for each unit or flotilla of ships. If when
a ship (or a unit) reached her allotted square, from which the line of
patrol extended, she elected to proceed on the _inner beat_, she would
generally accomplish the return journey to the point of departure on the
_outer beat_, thus covering her respective zone of patrol, but leaving
the exact route to the discretion of the commanding officer. In this way
no hostile submarine with a knowledge of the system could be sure of
when or where a patrol ship would be met. In the same way it was left to
the commander of a flotilla to either divide his ships into pairs,
single units, or to maintain them as a homogeneous fleet, so that any
combination of hostile submarines could not be made which would be sure
of being able to attack a _single_ patrol. Such an enemy combination
might encounter a single ship, but it might also walk into the arms of a
whole flotilla; or it might attack a single ship only to find itself
surrounded by a following fleet.
[Illustration: FIG. 22.--Diagram illustrating the operations of a
hydrophone flotilla composed of armed motor launches. Each vessel is
given a number, and the flotilla proceeds in line-abreast along the
course shown by the dotted lines. Each vessel is one mile from the
other, and the whole line stops by signal at the point marked with a
cross. Hydrophones are put in operation, and after a period of listening
the flotilla continues on its course, as no submarine sounds are heard.
The flotilla turns to head south, and a stop is again made to listen on
the hydrophones. This time the sound of a hostile submarine is heard by
vessel No. 1, bearing S.W. This report is confirmed by vessel No. 2
hearing the same sound, bearing a few degrees farther W. The two
bearings _A_ and _B_ are then drawn on a chart, and the point where the
two lines cross is the approximate position of the invisible submarine.
The attack with depth charges is then ordered.]
The beats which were most distant from the base were given to the
largest ships. This was done because it was often impossible for the
more distant patrols to reach a place of shelter before one of the
fierce gales which swept the northern seas was upon them. Trawlers,
large steam yachts and converted merchantmen were usually employed on
squares more than one hundred miles distant from a harbour of refuge,
while motor launches kept watch and ward on the seas closer inshore.
The duration of patrols varied according to their position. Some lasted
three weeks and others only a few days or hours. When the ships returned
to their base after a spell at sea they were given a corresponding
"rest" in harbour. A three weeks' patrol meant several days'
"stand-off," while a two or three days' patrol entitled the ship to
twenty-four hours in the comparative comfort of a harbour.
It must not be imagined, however, that a stand-off meant entire idleness
or thorough rest. There were duties to perform which robbed it of much
that it was intended to give. Ships had to be coaled, provisioned,
painted or repaired. Engines had to be overhauled, sentries posted
ashore, a guard to be furnished, and every day one ship in each unit
that was in harbour had to be manned and in readiness for emergencies.
HYDROPHONE FLOTILLAS
We now come to the actual methods employed by surface craft when
attacking submarines. Although, as previously stated, much was left to
individual initiative, there were, nevertheless, certain recognised
methods.
Taking as an example the operations of a hydrophone flotilla of armed
motor launches, the number of vessels forming the unit was usually five.
When out scouting for the enemy they proceeded in line-abreast for about
one sea mile, then stopped their engines and listened on their
hydrophones for the noise of a submarine cruising in the vicinity. If
nothing was heard the mile-long line of miniature warships advanced
another mile and again stopped to listen. This manoeuvre was repeated
until one or other of the ships heard the familiar sound of a U-boat.
Nothing might be visible on the surface of the sea, but if this was the
case and the noise came up from the ocean depths over the electrified
wires of the detector, it was conclusive proof that a submarine was in
the near vicinity.
The M.L. first detecting the noise hoisted a signal (flag by day and
coloured electric light by night), giving the direction from which the
sound came (see Fig. 22). The next ship in the line to receive the
sound on its instruments then hoisted a signal, also giving the
bearing--_i.e._ N.N.W., E.S.E., etc. If the two coincided in regard to
direction, the attack commenced. If, however, they did not agree in this
important respect, the line of patrol ships advanced another mile and
listened again.
The flag-ship of the unit on receiving the direction from one or more
ships marked the lines of sound on a chart (as in Fig. 22), and when
this was substantiated by another ship the point where the two lines
crossed was known to be the position of the hostile submarine, and the
attack was ordered.
As to the exact method of an anti-submarine attack little need be said
here beyond the fact that the ships advanced at full speed,
manoeuvring into a special formation which enabled them to cover about
half a square mile of sea with the explosive force of their collective
depth charges.
When the attack had been completed all vessels engaged resumed their
stations and waited with quick-firing guns ready in case the monster
should rise from the deep to make a dying effort to destroy her
pursuers.
The tactical methods of anti-submarine attack were, of course, numerous,
and they varied according to the speed of the surface ships engaged.
What was possible of accomplishment by fast-moving coastal motor boats
or the larger-sized M.L.'s proved impracticable for the more heavily
armed but slow-moving trawlers and drifters. The tactics of these
latter craft were often of the simplest character, and consisted
principally of either independent attacks with the aid of hydrophones
and depth charges, or, more frequently, the assumption of an innocent
air in order to induce the submarine to open the attack at close range.
[Illustration: THE RESULT OF A DIRECT HIT
A photograph left by the Germans in Ostend showing a coastal motor boat
washed ashore after the great raid.
_Thornycroft & Co., Ltd._]
In many respects this proved the most effective method of anti-submarine
warfare. Not only did it frequently cause the under-water craft to rise
to the surface and commence the attack by gun-fire, in order not to
expend a valuable torpedo on what appeared to be an unarmed and helpless
ship, but it also produced a _moral_ effect throughout the German
submarine flotillas.
When a few U-boats had been either sunk or damaged in this way the news
that every Allied ship was heavily armed circulated among the enemy
personnel, and they became very nervous of attacking in any position
except totally submerged. This meant the loss of at least one torpedo,
out of from five to ten carried, for every attack made, whether
successful or unsuccessful, and the latter were predominant.
It soon became apparent that either they must risk surface attacks and
so save their torpedoes, or else curtail their cruises to meet the rapid
expenditure of their only submarine weapon. This does not, of course,
cover the activities of under-water mine-layers, whose nefarious purpose
consisted simply of laying their mines wherever they appeared most
likely to catch Allied shipping. These craft were usually armed with
torpedoes as well as mines, to enable them to continue the work of
destruction when the cargo of the latter had been safely laid. In this
way the problem of combating the German submarine offensive resolved
itself into two parts, one being to checkmate the commerce raider and
the other the mine-layer. With the second of these difficulties we shall
deal in a later chapter.
Many merchantmen, both Allied and neutral, owed their escape to this
camouflage warfare, which was brought to a high pitch of perfection and
daring in the now famous mystery ships.
What may be said to form the second method of anti-submarine warfare was
the decoy or camouflage system. Of primary importance in this category
were the mystery ships already described, but there were also
innumerable other _ruses de guerre_ which increased its efficiency.
To describe one of these will enable the reader to draw on his own
imagination for the remainder. A vessel was steaming in from the
Atlantic and was about a hundred miles from the Cornish coast when she
was attacked by a submarine above water. The surface ship was heavily
armed, but instead of using her weapons at once she sent out frantic
wireless signals for assistance. Every few minutes the call went far and
wide in plain Morse.
The shells from the submarine splashed into the sea around, but none
struck the target for some minutes. Had the surface ship desired, she
could in all probability have avoided the under-water craft by using her
superior speed, but instead she dropped back, allowing the submarine to
catch up to her, and the shells began to burst unpleasantly close.
Still the frantic wireless calls went forth. First the simple message:
"I am being attacked by a large German submarine." Then the vehemence
increased to: "I am being heavily shelled." A few minutes elapsed and
then the call: "Help. Submarine gaining on me." And finally: "Abandoning
ship."
At this point the submarine was close astern and the liner slowing down
preparatory to lowering her life-boats. The shells were damaging her
superstructure, but a heavy swell interfered with the German
marksmanship. Then came the surprise. A life-boat on the liner's poop
was hoisted clear of the deck and from under its cover there appeared
the lean grey muzzle of a 4.7-inch gun. A few sharp blasts of cordite
and the submarine sagged and disappeared.
The captain of the liner had noticed when first attacked that the
submarine was fitted with wireless and the calls sent out by him were in
_plain Morse code_. On the strength of these the German commander had
saved his torpedoes but lost his ship.
* * * * *
Another form of anti-submarine tactics was the employment of indicator
and mined nets around an apparently disabled ship, or in lines across
narrow channels known to be used by German submarines on their way to
and from their bases. This method has, however, received full mention
in other chapters.
* * * * *
What may be termed the third system of anti-submarine warfare was the
use of extensive mine barriers, specially laid to catch submarines
attempting to pass through them under water. The surface of the sea was
patrolled by shallow-draft vessels and the under-seas guarded by mines.
If a submarine was sighted in the vicinity of one of the mine barriers
already described she was attacked and forced to submerge herself in
order to escape destruction from the guns of the pursuing surface
flotilla. From that moment her fate was sealed. By cautious
manoeuvring and using to full advantage their great superiority of
speed (20-40 knots against 6-10 knots) the surface ships were able to
head their quarry into the mine-field. Usually the submarine dived deep
in order to throw her pursuers off the track, and all unconscious of the
deep-laid mines in thousands she plunged to her doom--a heavy rumble,
followed by an upheaval of the surface, and the chase was over.
This method, when carried out on the vast and scientifically sound
principle described in a previous chapter, offers the best possible
antidote to the submarine. Its employment in the Great European War
placed the seal of complete success on the Allied anti-submarine
offensive. It should, however, be remembered that comparatively narrow
seas and a restricted zone of major operations made possible of
accomplishment with some hundreds of thousands of mines (average cost,
L400) what would in many cases and in many seas have been quite
impracticable with as many millions of these difficult weapons.
* * * * *
The employment of submarines against submarines also forms a method of
under-sea warfare which gives considerable scope for both daring and
resource. It is of course quite impossible for one of these vessels when
totally submerged to fight another in the same blind condition. But with
just the small periscopic tube--or eye of the submarine--projecting
above the surface, one craft can scout and watch for another to rise to
the surface, thinking no enemy is near, in order to replenish her air
supply for breathing or for recharging the electric storage batteries
which supply the current for submerged propulsion.
When such a position obtains the submarine which comes unknowingly to
the surface stands a grave danger of being torpedoed by her opponent.
This actually occurred to at least one German U-boat during the Great
War.
One or more submarines can also be employed around a slow-moving decoy
ship. In this case they would have the advantage of being invisible
until the actual moment of attack. The result of such a manoeuvre
would be either a gun duel on the surface or the torpedoing of the
attacking submarine by one or other vessel of the decoy's submerged
escort.
It was a ruse of this kind which achieved success in the North Sea
during the early stages of the war. A trawler was employed to tow a
submarine by a submerged hawser. This mode of progress was adopted to
enable the submarine to economise the strictly limited supply of
electricity carried for under-water propulsion.
The trawler then cruised very slowly about, dragging the submarine under
the surface behind her. In order to divert any suspicion which might
have been aroused by her slow speed she was rigged so as to give the
impression that a net was being towed, and the area of operations chosen
was well-known fishing-ground.
In this curious way days were spent before the desired consummation was
reached. Then a large U-boat came boldly to the surface and opened fire.
Instantly the submarine astern of the trawler was released from the tow
rope and forged ahead under her own electric engines. The commander of
the surface decoy stopped his ship and commenced lowering the small
life-boat carried. This was done in order to distract the attention of
the Germans from the tiny periscope which was planing through the water
to the attack.
A shell struck the trawler, carrying away her funnel, but did no other
damage, and a few seconds later the water around the U-boat rose up in a
vast upheaval of white. The plan had succeeded, and when the air cleared
of the smoke from the trawler's damaged stack there was nothing afloat
on the surface of the sea around--except an ever-widening patch of oil
and bubbles.
A few minutes later the thin grey line of the British submarine rose
above the swell some five hundred yards distant from the scene of her
triumph.
Another means by which one subaqueous fleet can attack another is by
laying mines in the seas around the enemy base.
* * * * *
These simple methods formed what may be termed the backbone of the
widespread anti-submarine operations during the Great War, but with the
experience gained and the brains of almost every nation focussed on the
problem of providing an effective counterblast to the under-water
warship, there can be little doubt that in the next great naval conflict
new and more scientific means of attacking these pests of the sea will
have been perfected, though what degree of success they will attain in
the stern trial of war the future alone can tell.[7]
FOOTNOTES:
[6] Greenwich mean time.
[7] For a careful study of the effect of the submarine on the old
theories of sea power see _Submarines and Sea Power_, by Charles
Domville-Fife (Messrs George Bell & Sons, Ltd., London, and Messrs
Lippincotts, New York.).