GETTING THE BEST OF THE U-BOAT
The U-boat commander who sallied forth from the harbor of Wilhelmshaven
in the early days of the war had nothing to fear. He was out to murder,
not to fight. His prey was always out in the open, while he could kill
without exposing more than his eye above water. Not even a sporting
chance was allowed his victims, particularly when he chose unarmed
merchantmen for his targets. He could come up boldly to the surface
and shell a ship into submission. This was cheaper than torpedoing
the vessel, because torpedoes are expensive. If the ship were speedy
it might run away; or if the U-boat came up too close to its intended
prey, the latter might run it down. That happened occasionally and it
was the only danger that the _Herr Kommandant_ had to fear.
If a destroyer suddenly appeared, the U-boat could dive into the
shelter of the sea. If the water were not too deep, it could lie on
the bottom for two or more days if need be. There was plenty of air in
the hull to sustain life for many hours, and then the compressed air
used for blowing the ballast-tanks could be drawn upon. In the U-boat
there were potash cartridges to take up the carbon-dioxide, and tanks
of pure oxygen to revitalize the air. If the submarine were damaged,
it was not necessary for it to come to the surface to effect repairs.
There were air-locks through which a diver could be let out of the
boat. He was fitted with oxygen and potash cartridges, so that he did
not need to be connected by an air-hose with the boat, but could walk
around it freely to mend injured rudders or to clear the propeller of
entanglements.
Even the small submarines of those early days were capable of taking
long voyages. Setting his course at a comfortable pace of 10 knots, the
U-boat commander could count on enough fuel to carry him 1600 miles,
and if need be he could slow down to 8 knots and by using certain of
his water-ballast tanks for additional oil-reservoirs, extend his
cruising-radius to nearly 3000 miles. The big 800-ton U-boats that
were built later had a radius of 5000 miles at an 8-knot speed. And so
when the British closed the English Channel with nets and mines, _Herr
Kommandant_ was not at all perturbed; he could sail around the British
Isles if he chose and make war upon transatlantic shipping. When
harbors were walled off with nets, he could remain outside and sink
vessels that were leaving or entering them.
SUBMARINE-CHASERS
A real menace came when the U-boat commander popped his periscope out
of the sea and saw several little motor-boats bearing down upon him.
They seemed harmless enough, but a moment's inspection showed them
to be armed with guns fully as powerful as those he carried. It was
useless to discharge a torpedo at so speedy and small a foe. A torpedo
has to have a fairly deep covering of water, else its course will be
disturbed by surface waves; and the submarine-chasers drew so little
water that a torpedo would pass harmlessly under them. It was useless
for the U-boat commander to come up and fight them with his guns. They
would have been upon him before he could do that, and their speed and
diminutive size made them very difficult targets to hit. Besides, he
dared not risk a duel of shell, for he knew that if the precious inner
hull of his boat were punctured, he could not seek refuge under water;
and if he could not hide, he was lost. The little armed mosquito craft
swarmed about the harbor entrances, ready to dash at any submarine that
showed itself. They could travel twice as fast as the submarine when
it was submerged and half again as fast as when it was running on the
surface.
Submarines had to take to cover when these chasers were about. _Herr
Kommandant_ did not even dare to take a look around through his
periscope, because the streak of foam that trailed in its wake would
betray him and immediately the speedy motor-boats would take up the
chase; and they had a disagreeable way of dropping bombs which, even
if they did not sink the submarine, might produce such a concussion as
to spring its seams. His foes had discovered one of his most serious
defects. He was blind under-water and they were making the most of this
handicap.
[Illustration: (C) Underwood & Underwood
Forward End of a U-boat. Note the Four Torpedo Tubes Behind the Officer]
Groping along under-water by dead-reckoning was not any too safe a
procedure near land, because he was liable at any moment to crash into
an uncharted rock or maybe into the wreck of some submarine victim. He
could not correct his bearings without coming to the surface, and, in
the black depths of the sea, a slight miscalculation might send him
to his doom. As was explained in the previous chapter, he had to keep
moving, because he could not remain suspended under water.
[Illustration: (C) Press Illustrating Service
A Depth-bomb Mortar and a Set of "Ash Cans" at the Stern of an American
Destroyer]
He was more helpless than a ship sailing in the densest of fogs. A ship
can stop and listen to sound-signals, or even to the beating of the
surf on the shore, or it can take soundings to locate its position; and
yet it is no uncommon occurrence for a ship to run ashore in a fog. How
much easier it is for a submarine to lose its bearings when obliged to
travel by dead-reckoning, particularly in the disconcerting excitement
of the chase! To avoid the danger of collision with surface vessels,
the commander chose to run at a depth of sixty-five feet. That was the
upper limit of his safety-zone. A depth of over two hundred feet was
his lower limit, because, as stated before, the water-pressure at that
depth would crush in his hull or at least start its seams. If the
bottom were smooth and sandy, and not too deep, he could settle gently
upon it and wait for darkness, to make his escape.
But while he lay on a sandy bottom, he was still in danger. Trawlers
were sweeping the bottom with nets. He might be discovered; and then if
he did not come up and surrender, a bomb would let in the sea upon him.
A HINT FROM NATURE
While he could not see under water, his adversaries could. They had
taken a hint from nature. The fish-hawk has no difficulty in spying
his submarine prey. Flying high above the water, he can see his
victims at a considerable depth, and wait his chance to pounce upon
an unwary fish that comes too near the surface. It is said that the
British trained sea-gulls to hunt submarines. Sea-gulls will follow a
ship far out to sea for the sake of feeding on refuse that is thrown
overboard. British submarines encouraged the birds to follow them, by
throwing out bait whenever they came to the surface. Of course the
birds could see the submarine even when it was submerged, and if they
pursued it, they were always rewarded with plenty of food. The gulls
drew no fine distinction between Hun and Briton, and so it came that
_Herr Kommandant_ often groped his way along in the dark sea, totally
oblivious of the fact that he was attended by an escort of feathered
folk who kept the British chasers informed of his presence.
In this connection it is interesting to note that the British trained
sea lions to hunt submarines. The animals were taught at first to swim
to a friendly submarine, locating it by the sound of its propellers.
They were always rewarded with fish. These sea lions were muzzled so
that they could not go fishing on their own account. Then they learned
to locate enemy submarines and pointed them out by swimming directly
toward them and diving down to them.
But there were human eyes, as well, that spied upon the U-boat. Fast
seaplanes patrolled the waters, searching constantly for any trace of
submarine. Its form could be vaguely outlined to a depth of from fifty
to seventy-five feet, unless the sea were choppy, and once it was
discovered, chasers or trawlers were signaled to destroy it with bombs
or to entangle it in nets. Often a submarine would be discovered by a
leak in its oil-tank which would leave a tell-tale trail. Sometimes
when the U-boat itself could not be discerned, there would be slight
shimmer, such as may be seen above a hot stove, caused by refraction of
light in its wake. This was easily recognized by trained observers.
[Illustration: (C) Press Illustrating Service
A Depth-bomb Mortar in Action and a Depth-bomb snapped as it is being
hurled through the air]
Even better aërial patrols were the small dirigibles known as Blimps.
They are a cross between a balloon and an airplane, for they have the
body and the power-plant of an airplane, but the planes are replaced by
a gas-bag. Blimps could cruise leisurely and search the sea thoroughly.
They could stop and hover directly over a submarine and drop explosives
upon it with great accuracy. And so _Herr Kommandant_ could take no
comfort in hiding under a blanket of waves unless the blanket were so
thick as to conceal his form completely from the eyes overhead. This
made it imperative to leave the shallower waters near shore and push
out into the deep sea, where the small chasers could not pursue him.
But he could not shake off his pursuers. Stream-trawlers are built
to ride the heaviest gales and they took up the chase out into the
ocean.
[Illustration: Courtesy of "Scientific American"
Airplane Stunning a U-boat with a Depth-bomb]
There was a decided advantage for the U-boat in moving out to sea. It
had a wider field of activity and could more easily escape from its
pursuers. But on the other hand, its prey also had an advantage. Out in
the open ocean they were not obliged to follow the usual ship lanes and
it was more difficult for a submarine to intercept them. There it took
more U-boats to blockade a given area.
A GAME OF HIDE-AND-SEEK
Then, it ceased to be quite so one-sided a game when merchantmen began
to carry guns. That made it necessary for the submarine commander to
creep up on his victims stealthily, and depend upon his torpedoes. He
had to get within a thousand yards of the ship and preferably within
five hundred yards, in order to be sure of hitting it. If the ship
could travel faster than he could, he had to do this without betraying
his presence. But ship-captains soon learned that their safety lay in
zig-zagging. When _Herr Kommandant_ reached the point from which he
had planned to attack, he would raise his telescopic periscope out of
the water, expecting to see his victim within good torpedo range, only
to find it sailing safely on another tack. Again, he would have to take
observations and make another try, probably with no better luck. It was
a game of hide-and-seek in which the merchant ship had a good chance of
making its escape, particularly when blotches of camouflage paint made
it difficult for him to get the range, as described in Chapter XI.
[Illustration: Courtesy of the Submarine Defense Association
FIG. 19. How a ship hid behind smoke produced on its own stern, with
different directions of wind]
Slower ships could be attacked without all this manoeuvering, provided
the submarine's guns outranged those of the ship. And so U-boats
were provided with larger and larger guns, which made it possible
for them to stand off and pound the merchantmen while out of reach
of the vessel's guns. But ships found a way of hiding on the surface
of the sea. A vessel would spout forth volumes of dense black smoke
which would obliterate it from view. (See Fig. 19.) If the wind was
quartering, the ship would change its course and dodge behind the
sheltering pall of smoke. Not only was the smoke produced on the
vessel itself, but smoke-boxes were cast overboard to form a screen
behind the vessel. These smoke-boxes contained a mixture of coal-tar
and phosphorus and other chemicals which would produce incomplete
combustion. They were ignited by the rubbing of a phosphorus compound
on a priming-composition, and then cast adrift to pour out dense
volumes of heavy smoke. (See Fig. 20.) Behind this screen, the ship
could dodge and zig-zag and if her speed were greater than that of the
submarine, her chances of escape were very good.
[Illustration: Courtesy of the Submarine Defense Association
FIG. 20. How a ship hid behind a screen of smoke produced by throwing
smoke-boxes overboard]
Another annoyance that _Herr Kommandant_ experienced was, when he
lifted his periscopic eye above water, to find it so smeared with a
sticky substance that he could not see. His foes had strewn the water
with tar-oil that had spread in a thin film over a surface miles in
extent. This blinded him at first, but before long he was equipped
with a jet for washing off the periscope glass and that little
annoyance was overcome.
But the craft most dreaded by the U-boat commander were the destroyers.
These light, high-powered, heavily armed vessels could travel twice as
fast as he could on the surface and three times as fast as he could
submerged. Shells were invented which would not ricochet from the
surface of the sea, but would plow right through the water, where they
struck and hit the submarine below water-level.
DEATH-DEALING "ASH CANS"
However, it was not shell-fire that he dreaded, but the big "ash cans"
loaded with TNT which were timed to explode far under water, and which
would crush his boat or start its seams. It was not necessary for these
bombs to hit the U-boat. When they went off they would send out a wave
of pressure that would crush the boat or start its seams even if it
were a hundred feet and more from the point of the explosion. Within
limits, the deeper the explosion the wider would its destructive area
be.
The timing-mechanism of some depth bombs consisted merely of a float
on the end of a cord. When the bomb was thrown overboard this float
remained on the surface until the cord was pulled out to its full
length, when there would be a yank on the firing-trigger and the charge
would explode. In other depth bombs there was a valve operated by the
pressure of the water. When the bomb sank to the depth for which the
valve was set, the pressure of the water would force the valve in,
exploding a cartridge which set off the charge. So powerful were these
depth bombs that the destroyer had to travel at high speed to get out
of range of the explosion.
Depth bombs were rolled off the stern of the destroyer and also thrown
out from the sides of the vessel by means of mortars. Some of the
mortars were Y-shaped and held a depth bomb in each arm of the Y. When
a blank 3-inch shell was exploded at the base of the gun, both bombs
would be hurled from the ship, one to port and the other to starboard.
In this way the destroyer could drop the bombs in a "pattern" of wide
area. _Herr Kommandant_ gained a wholesome respect for these terriers
of the sea. It was suicide to show himself anywhere near a destroyer.
In a moment the speedy boat would be upon him, sowing depth bombs
along his course. His chances of escaping through this hail of high
explosives were remote indeed.
The ships that he was most eager to destroy were either too speedy for
him to catch, unless they happened to come his way, or else they were
herded in large convoys protected by these dreaded destroyers. The
convoy proved a most baffling problem for _Herr Kommandant_. He dared
not attack the convoy by daylight. In a fog he might take a chance at
picking off one of the ships, but even that was very risky. He could
trail the convoy until dusk and then under cover of darkness draw near
enough to discharge a torpedo, but in the daytime he must keep his
distance because there were eyes in the sky watching for him. At the
van and rear of the convoy there were kite balloons high in the sky,
with observers constantly watching for periscopes, and for U-boats that
might be lurking under the surface.
As the destroyers gained in experience, the difficulties of the U-boat
attack grew greater and its work grew more and more perilous. The crew
grumbled and grew mutinous. The morale of the men was shaken. We can
imagine the horror of plunging hurriedly into the depths of the sea,
and rushing along blindly under the surface, dodging this way and that,
while terrific explosions of depth bombs stagger the submarine and
threaten to crush it, and there is the constant expectation that the
next explosion will tear the thin shell of the U-boat and let in the
black hungry water. The tables were turned. Now, if never before, _Herr
Kommandant_, the hunter, knew what it felt like to be hunted.
[Illustration: (C) Underwood & Underwood
The False Hatch of a Mystery Ship and--]
[Illustration: The same Hatch opened to disclose the 3-Inch Gun and
Crew]
It takes an exceptional man to go through such a harrowing experience
with unshattered nerves. On at least one occasion, a submarine that
was being depth-bombed came suddenly to the surface. The hatch flew
open and the crew rushed out, holding up their hands and crying,
"_Kamerad_." The U-boat was uninjured, but the shock of a depth bomb
explosion had put the electric-lighting system out of commission, and
the crew, unnerved by the explosion and terrified by the darkness, had
overpowered their officers and brought the boat to the surface.
[Illustration: A French Hydrophone Installation with which the presence
of Submarines was detected]
EYES IN THE SEA
There were other craft that _Herr Kommandant_ had to look out for. His
were not the only submarines in the sea. His foes also were possessed
of submarines. They could not see under water any better than he could,
but they could fight on the surface as well as he, and they could
creep up on him even as he crept up on his prey. As a French submarine
commander puts it: "The U-boats used to enjoy the advantage of
remaining themselves invisible while all the surface and aërial craft
which were sent in pursuit of them were boldly outlined against the sky
and visible to them. This is one of the reasons we used submarines to
ambush U-boats." Submarines were also used to accompany the convoys,
so that the U-boat commander had to watch not only for the eyes of the
ship's lookouts and the eyes in the kite balloons, but also for the
periscope eyes that swam in the sea.
TRAILING U-BOATS BY SOUND
The troubles of the submarine-commander were multiplying. All over
the world inventors were plotting his destruction. As long as we
depended upon our eyes to ferret him out, the sea was a safe refuge,
provided he dived deep enough, but when we began to use our ears as
well, he found himself in a very serious predicament. Although light is
badly broken up in its passage through water, sound-waves will travel
through water much better than in air. The first listening-devices used
were crude affairs and did not amount to much, particularly when the
U-boats muffled their motors and engines so that they were virtually
noiseless. But the French invented a very sensitive sound-detector. It
consisted of a lot of tiny diaphragms set in a big hemisphere. There
were two of these hemispheres, one at each side of the boat. When
sound-waves struck these hemispheres, the diaphragms would respond. At
the focus of each hemisphere there was a megaphone receiver; one of
these carried the sound to the operator's right ear and the other to
his left. He would turn a megaphone around until he found the diaphragm
that produced the loudest sound. This gave him the direction of the
sound-wave. Then the boat would be steered in that direction. He knew
that it was aimed properly when the sound coming to his right ear was
just as loud as that which came into his left ear.
A still better hydrophone was developed by a group of American
inventors. The details of this cannot yet be disclosed, but we know
that it was adopted at once by our allies. A very sensitive receiver
was used which could detect a U-boat miles away and determine its
direction accurately. Under ideal conditions the range of the device
was from fifteen to twenty-five miles, but the average was from three
to eight miles. If two or more boats fitted with sound-detectors were
used, they could determine the position of the U-boat perfectly. One
drawback was that the vessel would have to stop so that the noise of
its own engines would not disturb the listener, but this was largely
overcome by trailing the detector a hundred feet or more from the stem
of the ship. The sounds were then brought in by an electric cable to
the listener in the ship.
These sound-detectors were placed on Allied submarines as well as
surface vessels and they were actually tried out on balloons and
dirigibles, so that they could follow a U-boat after it had submerged
too deeply to be followed by sight.
[Illustration: Courtesy of the "Scientific American"
FIG. 21. Chart of an actual pursuit of a U-boat which ended in the
destruction of the submarine]
[Illustration: Section of a captured Mine-laying U-boat, showing how
the mines were laid]
Many U-boats were chased to their doom by the aid of the American
hydrophone. Fig. 21 illustrates a very dramatic chase. The full line
shows the course of the U-boat as plotted out by hydrophones and the
broken line the course of the submarine-chasers. The dots represent
patterns of depth bombs dropped upon the U-boat. Try as he would, the
_Herr Kommandant_ could not shake off his pursuers. At one time, as the
listeners stopped to take observations, they heard hammering in the
U-boat as if repairs were being made. The motors of the submarine would
start and stop, showing clearly that it was disabled. More depth bombs
were dropped and then there was perfect silence, which was soon broken
by twenty-five revolver-shots. Evidently the crew, unable to come to
the surface, had given up in despair and committed suicide.
[Illustration: (C) Underwood & Underwood
A Paravane hauled up with a Shark caught in its jaws]
The Adriatic Sea was an ideal place for the use of the hydrophone. The
water there is so deep that submarines dared not rest on the bottom,
but had to keep moving, and so they could easily be followed. Across
the sea, at the heel of the boot of Italy, a barrage of boats was
established. U-boats would come down to this barrage at night and,
when within two or three miles of the boats, dive and pass under them.
But when hydrophones were used that game proved very hazardous. Our
listeners would hear them coming when they were miles away. Then they
would hear them shift from oil-to electric-drive and plunge under the
surface. Darkness was no protection to the U-boats. The sound-detector
worked just as well at night as in the daytime and a group of three
boats would drop a pattern of bombs that would send the U-boat to the
bottom.
On one occasion after an attack it was evident that the submarine had
been seriously injured. Its motors were operating, but something must
have gone wrong with its steering-gear, or its ballast-chambers may
have been flooded, because it kept going down and soon the listeners
heard a crunching noise as it was crushed by the tremendous pressure of
the water.
And so U-boat warfare grew more and more terrible for _Herr
Kommandant_. The depths of the sea were growing even more dangerous
than the surface. On every hand he was losing out. He had tried to
master the sea without mastering the surface of the sea. But he can
never really master who dares not fight out in the open. For a time,
the German did prevail, but his adversaries were quick to see his
deficiencies and, by playing upon these, to rob the terror of the sea
of his powers. And as _Herr Kommandant_ looks back at the time when he
stepped into the lime-light as the most brutal destroyer the world has
ever seen, he cannot take much satisfaction in reflecting that the sum
total of his efforts was to spread hatred of Germany throughout the
world, to summon into the conflict a great nation whose armies turned
the tide of victory against his soldiers, and finally to subject his
navy, second only to that of Great Britain, to the most humiliating
surrender the world has ever seen.