SOME CURIOUS WEAPONS OF ANTI-SUBMARINE WARFARE
ALTHOUGH modern war has shown that there exists no certain antidote for
the submarine, it nevertheless brought into being many curious weapons
of attack and defence. It is the purpose of this chapter to describe
some of the anti-submarine devices used with more or less successful
results during the protracted naval operations against the Central
Powers.
INDICATOR NETS
Among the most important of these were the immense meshes of wire known
as "indicator nets," which were used to entangle a submarine and then to
proclaim her movements to surface ships waiting to attack with guns and
depth charges.
[Illustration: FIG. 11.--Diagram showing principal features of a line of
submerged indicator nets. _AA._ Two sections (100 feet in breadth) of
thin wire-netting with a very wide mesh. _B._ Framework of wire rope
holding each section of net in place by means of metal clips _C_. _C._
Metal clips which expand and release netting from rope frame when a pull
of more than 100 lb. is exerted upon them. _D._ Line of invisible glass
balls, or hollow floats, attached to a surface wire _E_, supporting by
wires _F_, the nets which hang down from the surface vertically in long
lines (1/2 to 1 mile in length and 50 feet deep). _G._ Heavy iron
weights or sinkers holding down the nets by their weight when hanging in
water. _H._ Wooden floats, attached to each section of net by wires _I_.
_J._ Canisters of chemical which give off flame and smoke when exposed
to sea-water. _K._ Lanyard attached to surface wire _E_. When a section
of net is pulled out of its wire frame by a submarine passing through
the line the float is dragged along the surface by the wire _I_. The
lanyard is held back by being attached to surface wire _E_, and pulls a
plug out of the canister _J_, exposing the chemical inside to the
sea-water (see Fig. 12).]
These nets were made of specially light but strong wire, with a mesh of
several feet. They were joined together in lengths of 100 feet by metal
clips which opened when a certain strain was exerted on any particular
section. Their depth was usually about 50 feet, and they were laid in
lengths varying from a few hundred yards to two miles. Weights at the
lower end and invisible glass floats along the top held them suspended
vertically from the surface. The floats were kept in place by a wire
hawser running along the top of the nets, and to this were attached, at
intervals, wooden buoys containing tin cases filled with a chemical
compound which, when brought into contact with sea-water, emitted dense
smoke by day and flame by night.
The 100-feet sections were linked together, and to the top and bottom
ropes, by the metal clips. These clips opened when a submarine headed
into that part of the line. The result was that a section of net
enveloped the bow of the under-water craft, was detached from the line
and carried along, dragging its _indicator float_ on the surface behind.
The indicator float, containing the chemical, was attached (1) to the
section of net by a short wire and (2) to the top rope of the whole line
by a lanyard, which, when pulled free, exposed the chemical contents of
the canisters in the float to the sea-water. The float was then dragged
along the surface burning furiously.
As there was nothing to materially impede her progress, a submarine
would consequently be unaware that she had passed through a line of nets
and was actually towing a flaming buoy. Even if she became aware of the
tell-tale appendage it would be extremely difficult to clear herself,
owing to the forward hydroplanes becoming entangled in the wire-netting,
before the fast surface ships, waiting in readiness, had spotted the
flaming buoy being towed along and were hot in pursuit.
Once entangled in such a net, the submarine's chance of avoiding
destruction was small. Not only did the indicator buoy proclaim her
every movement to the pursuing surface ships, so that she could not
avoid them by turning, sinking to the bottom or doubling in her tracks,
but it also enabled depth charges to be literally dropped on her decks.
[Illustration: FIG. 12.--Diagram showing a submarine entangled in a
submerged net. The submarine _A_ after passing through a line of nets
emerges with her bows enveloped by one section _B_ which she has carried
out of its wire-rope frame. The flaming buoy _C_, betraying her
movements, is being towed along the surface.]
A considerable measure of success attended the use of this ingenious
device until "Fritz" became shy of waters close inshore, and kept a
careful look-out for possible lines of indicator nets when forced to
pass through narrow channels and waterways. One of the main
disadvantages attending the use of these nets was the impossibility of
laying them--or, when laid, of hauling them inboard again, during even
moderately rough seas. Another difficulty which presented itself when
indicator nets were required to be laid in the open sea was the
screening of the waiting surface ships from observation. Submarines
could not be used on account of their slow speed, and when fast patrol
craft cruised about openly within easy range of the nets "Fritz"
suspected a trap and steered clear. Even this, however, had its uses.
MINE NETS
It was sought to overcome this difficulty by attaching small explosive
mines to the nets instead of indicator floats, so that when a submarine
passed through a line she unavoidably struck one or other of the
attached mines, which instantly exploded.
This device also proved fairly successful, but the dangers of handling
mined nets were considerable and disasters resulted. Furthermore, as
such obstructions could not be securely moored in one spot for very
long, owing to the action of gales and strong tides, it became necessary
for the sake of neutral and allied shipping to maintain a vessel in the
vicinity from which warnings could be issued and repairs to the nets
effected. This partly defeated the object of mined nets, except for the
closing of narrow fair-ways, and their scope as a weapon of attack
became strictly limited.
THE MODIFIED SWEEP
This elaborate and costly anti-submarine device was very widely, but not
altogether successfully, employed by the auxiliary fleet during the
first two years of war. It was nothing more than a long explosive tail
towed submerged by a surface ship, the object being to either drag it
over a submarine resting on the sea-bed, or else, if the under-water
craft was moving, to so manoeuvre the towing surface ship as to swing
the tail close to the U-boat, when the heavy charges of T.N.T. attached
to the armoured electric cable, forming the tail, would be exploded
either by actual contact with the hull of the enemy, or, when
sufficiently close to be effective, by the closing of a firing circuit
on board the surface ship.
[Illustration: FIG. 13.--Diagram showing a vessel towing a modified
sweep. This appliance consists of an armoured electric cable _G_ towed
in vertical loop under the surface. The floats _D_ support the 100-lb.
charges _E_, which have strikers attached. If a submarine _B_ is lying
"doggo" on the sea-bed one or other of these charges may strike her hull
and the whole line then blows up, shattering everything in the
surrounding sea. If the strikers fitted on the charges do not touch the
submarine the whole line can be exploded at will from the surface ship
by closing an electric circuit.]
Excellent in theory but very difficult of accomplishment in actual
practice. The diagram given will explain the details of this elaborate
contrivance, which, however, was soon discarded for more practical
methods, although at least one German submarine is known to have been
destroyed by it.
LANCE BOMBS
These little engines of destruction were intended for fighting at close
quarters, and can be described here in a few lines because of their
guileless simplicity. They consisted of conical explosive bombs on the
ends of broom handles! A strong man could whirl one of them round his
head, like a two-handed sword or battle-axe, and, when the momentum was
sufficient, hurl it over the water for about seventy-five feet. On
nose-diving into the sea and hitting the hull of a submarine in the act
of rising or plunging, the little bomb, containing about 7 lb. of
amatol, was exploded by contact.
[Illustration: FIG. 14.--A lance bomb. The wooden handle _A_ enables the
charge _B_ (7 lb. of high explosive) to be whirled round the head and
hurled a distance of about twenty yards.]
The damage inflicted on one of the earlier types of submarines by an
under-water hand-grenade or lance bomb depended entirely upon what part
of the vessel happened to be struck. Their sphere of usefulness was,
from the first, very limited, and the advent of the big cruiser
submarine, with armoured conning-tower and 5-inch guns, rendered them
obsolete.
SMOKE SCREENS
We now come to a more useful device of the purely defensive type
employed to screen surface ships from submarine attack. The very simple
mechanical and chemical apparatus needed for making the heavy clouds of
smoke needs no description beyond that given in the text, but something
must be said here regarding the methods of use.
It was not until the third year of the Great War had been ushered in by
the unprecedented sinking of Allied merchantmen by German U-boats that
the value of the smoke screen as a means of baffling an under-water
attack was fully realised. Convoy guards were supplied with the
necessary appliances for emitting the fumes with which to cover the
movements of the ships under their protection, and so successful was
this method of blinding attacking submarines that within a few months
thousands of transports, food-ships and warships had been equipped.
When a submarine proclaimed her presence in the vicinity of a convoy
either by showing too much of her periscope or by a misdirected torpedo,
the guard-ships on the flank attacked immediately dropped their smoke
buoys as they continued moving at full speed. By this means an
impenetrable optical barrier was interposed between the attacking
submarine and the fleet of merchantmen under convoy. When thus shielded
from attack--a submarine values her small stock of torpedoes (six to
ten) too highly to risk the loss of one or more on something she cannot
even see--the mercantile fleet altered course so as to present their
sterns to the attacking U-boat, while certain prearranged warships
belonging to the escort proceeded to the attack with guns and depth
charges.
This means of masking the movements of ships--by no means new in naval
warfare--was employed with conspicuous success in the operations of
Allied squadrons off Zeebrugge. Individual merchantmen, when attacked by
one or more submarines, often threw out a smoke screen to avoid
destruction by the big surface guns of the more modern German craft, and
its use to cover the movements of transports was very frequently
resorted to.
CAMOUFLAGE
The use of camouflage, or the deceptive painting and rigging of ships,
came first into being owing to the method employed by submarines for
judging the speed of passing surface ships by the white wave thrown off
from their bows. It is of the utmost importance for the commander of an
under-water warship to correctly judge the speed of the vessel he is
about to attack before discharging a torpedo at her. If the estimated
speed is too high the torpedo will, in all probability, pass ahead of
the moving target, and if it is too low it will run harmlessly astern.
To cause this to happen as frequently as possible, and valuable
torpedoes to be wasted--even if the attacking submarine herself could
not then be discovered and destroyed--it became advisable to paint
imitation white waves on the bows of slow-moving ships in order to give
the appearance of speed.
[Illustration: FIG. 15.--A camouflaged ship. It will be observed that a
vessel so painted would, from a distance of several miles, give the
appearance of a ship sinking while headed in the opposite direction.]
So successful was this simple form of deceptive paint-work that a
special camouflage section of the naval service, with an eminent artist
as its director, was formed, and all kinds of grotesque designs were
painted on the broadsides and superstructures of almost every British
merchantman operating in the submarine danger zone.
There was method and meaning in the seemingly haphazard streaks of
black, green, blue and white. When looked at from close range only a
jumble of colours could at first be seen, but if the distance was
increased the effect became instantly apparent. In some cases the
deceptive decoration caused big ocean liners to appear small and
insignificant. In others it gave the appearance that the vessel was
sinking; while quite a favourite ruse was to cause the vessel to appear
as if she was travelling in the opposite direction to that which she
really was. Two-funnelled ships became single-funnelled, when viewed
from a distance or in a dim light, by the simple expedient of painting
one funnel black and the other light grey. Liners with tiers of
passenger decks had the latter obscured by contrasts of colouring which
were really masterpieces of deceptive art. In fact so deceptive became
almost every ship in the dim light of dawn and dusk that collisions were
often narrowly averted.
It frequently occurred that paint alone was not sufficient to disguise a
ship, and woodwork and canvas were resorted to. Big guns were made of
drain-pipes and shields of the wood from packing-cases. Cargo boats were
given the appearance of cruisers, and cruisers reduced to the appearance
of cargo boats. In this way hostile submarines were induced to attack
ships, thinking them unarmed and helpless, when in reality they were
small floating forts. But at this point simple camouflage ceases and the
famous _Mystery Ship_ begins. Before closing this chapter, however, it
must be pointed out that camouflage only came into being when the German
U-boats commenced their ruthless submarine warfare.