Confident that the sonar department's
equipment were functioning well and the crew had gotten the hang of finding
targets, the admiral decided to conduct a practice attack. SS Heimlich was to
sail around the exercise area and U-1215 was to find her and fire one of their
practice torpedoes. These had the same propulsion system and sensors as the
live ones and were tipped with a rubber head. When they hit, the target's hull
would give a loud boom. Heimlich, on the other hand, had dummy hedgehog
projectiles. These also made a loud booming sound when they hit. If either
vessel was hit, that would signal the end of the exercise. The admiral was
going to be inside the submarine to gauge U-1215's, and her crew's,
performance.
It was going to be a duel between a new
submarine and a seasoned hunter. It was also a duel between a mostly green crew
and a crew of veterans. The only advantage that U-1215 had was her silent
propulsion and silent weapons.
On 24th April, U-1215 slipped out of her
sub pen and set out for the exercise area. SS Heimlich was already at sea,
having left earlier.
The exercise area was far out to sea but
other u-boats sometimes passed through it either on the way out to their patrol
assignments or in coming back to base. To avoid complications, the admiral had
a false message sent out saying that the area had been mined and that all
u-boats were to avoid it. They would have to detour around that patch of sea,
giving U-1215 and Heimlich the privacy they needed for their exercise.
Previously, Heimlich had been unable to
detect the secret sub. She had stayed some distance away as U-1215 conducted
her trials. In the last one, where U-1215 tried to track the Heimlich and a
small merchant vessel, Heimlich had actually heard the submarine when he
happened to turn toward it, forcing them to dive quickly. Diving causes a sub's
hull to pop or generate soft booms and that is what gave them away. After that,
however, nothing else was heard. That sub was certainly quiet. They were going
to have to be creative.
U-1215 crept into the exercise area at
engines ahead one-third. The sub hardly made any sound especially at this
speed. About the noisiest equipment in the sub was the reactor coolant pump but
that was mounted on rubber stands and springs which prevented any vibrations it
made from reaching the hull. The only way to make a sound was for someone to
drop something onto the metal grating that passed for a floor in a submarine.
Their shoes had soft rubber soles that kept their footfalls quiet and
everything that wasn't supposed to be moving was secured or tied down.
The Heimlich's commander was being smart.
She was lying on the surface with her engines off. Her sonar was set to
passive, just listening without producing any sound herself. All the crew were
told to move quietly about their duties or stand still. Talking was not
forbidden but a warning had been issued about shouting, something about being
shot or thrown overboard. This was a matter of pride for both vessels.
Heimlich's sonar man looked like he was in
a trance, his face blank and with a faraway look in his eyes. He was
essentially blind during times like this. The only way to catch his attention
was to talk to him. Standing or sitting in front of him wouldn't work. They
usually refrained from touching him as it sometimes startled him. So intent on
listening to sounds in the sea, his hearing practically took over his whole
being.
The sonar operators on U-1215 went about
their job in much the same way. To help them concentrate, U-1215 was rigged for
silent running. It was easier to hear from underwater than from above it since
water conducts sound much better than air. Werner wasn't taking chances,
however. Every order or report was given sotto voce. Everyone was either
sitting or standing still.
The submarine was actually about 10
kilometers from the Heimlich but both of them had not heard each other. Werner
now knew the destroyer was lying to, her engines stopped and her sonar people
listening intently. He didn't know where his quarry was. He was tempted to use
the periscope but the point of the exercise was to see if they could detect and
evade using just the sonar.
For the good part of an hour, both vessels
just listened for each other. At one point, U-1215 actually passed within 500
meters of the Heimlich but neither of them heard the other. One of them was
going to have to make a mistake or something happened that would give one of
them away. U-1215 was more fortunate in that she was underwater. Heimlich, on
the surface, was starting to feel the effects of an approaching squall.
The wind was rising and the waves were
starting to slap against the destroyer's hull. They were starting to make noise
that a good sonar operator could hear. Heimlich's commander knew this and was
thinking of starting his engines anyway when his sonar man reported a loud
crashing sound. The rolling of the ship had caused something large to drop to
the ship's steel flooring. The commander didn't need the report to know about
it. The noise was that loud.
Heimlich was quick to react. Her engines
were started up and she began moving about. Her quarry was still undetected but
he was free to use his active sonar if he saw fit.
U-1215
The U-1215's sonar man suddenly straightened
up. The noise was too clear to be far away. Just as he was about to report it,
he heard the destroyer's engines start up. The game was on.
"Captain, noise transient at bearing
345°. Now hearing engine and screw noises. It's the Heimlich, sir."
Werner came over to the sonar room and
waited for the next report. All he knew was that the Heimlich was to his north.
He didn't know how far away or whether it was coming toward or away from him.
The other sonar man rotated his directional sensor and found his target.
"Heimlich is now at bearing 343°,
estimate distance 1,600 meters."
Listening to his sonar men was a test of
patience. They had a direction and a rough range but they didn't know what
direction the target was moving. They listened intently to the sounds and made
educated guesses. If the sound was growing fainter, the target was moving away.
If it was getting stronger, it was moving toward them. That much was easy to
do. Getting a course was much more difficult. Heimlich wasn't going to make it
easier though.
"ASDIC! She's using her active sonar.
Sound's faint though. She's turning around...away from us." The man's
halting, short sentences was how they made their reports.
Heimlich was sending pings into the water
to try and acquire U-1215. She was pointed in the wrong direction for now but
she was turning slowly to sweep the sea around them. Time to do some
maneuvering.
"Make your course 160°." Werner
was going to move directly away from the destroyer. Also, by putting the
destroyer on his tail, he reduced his profile from the destroyer's sonar.
Hopefully, it would be small enough for the sonar man on Heimlich to ignore it.
SS HEIMLICH
Heimlich's sonar man listened intently for
the returning pings from the active sonar. Her active sonar sent out short,
directional bursts of sound into the water. The sound traveled through the
water and, when it hits an object, is reflected back to the source. The time
difference from the start of the sound burst and its return gave a fairly
accurate range to the object that reflected it. The strength of the returning
echo told the sonar man how large or hard the object was. A small echo could
probably mean a large fish or dolphin. A large return that sounded muffled was
probably a school of fish. A rather large and solid return might turn out to be
a whale…or a submarine.
As the destroyer continued her turn, the
sonar operator heard a few faint returns that were close. Fishes. A somewhat
larger return occurred as the ship was pointed toward the south. It was a
little too small for a submarine but the man had been working with sonar for
several years and was good at it. He reported the contact to the captain.
U-1215
"Control room, he's turning back! He
might have gotten a return off us." The sonar operator on U-1215 dialed in
his controls. The Heimlich's engine sounds changed to a higher note as the
destroyer sped up to get on top of the submarine. "He's coming toward
us."
Werner knew Heimlich was faster than U-1215
even at flank speed so trying to outrun her was pointless. His advantage,
however, was that Heimlich could only listen in one direction, the front. He
thought fast.
Sonar estimated Heimlich was moving toward
U-1215 at 15 knots. At this distance, she'd be over him in a little more than
three minutes. U-1215, however, was moving away from her at 10 knots so the
closure rate was actually five knots which meant Heimlich would catch up with
them after about 10 minutes. He had time. "Dive! Make your depth 120
meters. Maximum dive rate."
He was going to go deep. As the submarine
dived, the temperature of the surrounding water suddenly changed several
degrees in a few feet. This temperature change was called a "layer"
by submariners and submarine hunters. It tended to reflect sonar pulses so
submarines frequently used it to hide from the searchers.
There was another advantage to going deep.
It put vertical distance between the submarine and the destroyer. Depth charges
took longer to sink and made timing the drops more complicated.
S.S. HEIMLICH
Heimlich was carrying weapons. Hedgehogs
were mortar-like weapons that fired 24 shells in front of the ship. The shells
then entered the water and sank rapidly down into the depths. Unlike depth
charges, the hedgehogs were a contact-type weapon meaning, they had to actually
hit the submarine before exploding. An explosion after firing the hedgehog was
a sure sign that the submarine had been hit.
Of course, Heimlich would only use dumbed
weapons on this target. They were on the same side after all. The hedgehogs
were fitted with a dummy head and won't explode when they hit the hull of the
sub.
Heimlich bore straight for the echo showing
on his sonar. The pulses were changing which told the sonar man that his target
was diving. The distance was great but their speed might put them above the sub
before it disappeared underneath the layer. A hedgehog fusillade would be fired
and when the boom of even one shell is heard, the exercise would end.
U-1215
U-1215 was canted downwards at such a steep
angle that her crew held on to whatever was close by to keep from sliding down
towards the bow. Werner kept his eye on the bathythermograph, a device that
measured the temperature outside the submarine and plotted it on a roll of
paper as a long unbroken line. He smiled as the line suddenly moved signaling
that there was a rapid change in temperature. They had reached the layer.
"Slow to one-third, level out at 115
meters. Once we're level, give me fifteen degrees right rudder. Come to new
course 290°."
He was turning right to confuse his
pursuer. His pursuer could no longer hear him and would have to decide if the
sub had turned left, right or stayed on course. One in three odds could not
instill confidence but it was better than nothing.
S.S. HEIMLICH
Heimlich's captain cursed under his breath
when his sonarman reported that contact had been lost. The sub could have
turned anywhere but, from experience, a sub would usually either turn left or
right. Rarely did they maintain course. The captain did a mental coin toss and
made his decision.
"Slow to one-third. Come right to
250°."
U-1215
Both vessels had made a right turn but
U-1215 had continued her turn until she was a little to the north of Heimlich
who was moving west-south-west while U-1215 headed west-north-west. With U-1215
underneath the layer, both vessels couldn't hear each other and were
essentially blind. Werner, thought quickly. If Heimlich had turned left, he was
to his east and moving away. If he had gone straight, they were also heading
away from each other. If he had changed course to the right, he was probably a
little to the south or right above him. Werner's best option was to make
another turn to the right. That move would either bring them further apart or
maintain their distance.
"Come right, change course to
070°"
S.S. HEIMLICH
Heimlich maintained her course, his active
sonar pinging away at the sea. Hunting for submarines was a waiting and
guessing game. Patience was often rewarded though patience in this game was
sometimes measured in hours and Heimlich's captain was a patient man.
S.S. Heimlich had a reputation among both
German and Allied submarines. She had sent several British submarines to the
bottom of the ocean and harried a lot of German u-boats on their approach or
departure to and from their submarine bases in the Atlantic coast of France. He
was good at what he did and there were few German u-boat captains who could
surprise him.
That accursed submarine
could be anywhere, thought Heimlich's commander.
She was very quiet and his sonar operator had not heard her except for a hull
pop when she changed depth. His best hope of finding her was to use his active
sonar but the submarine could also hear the sound pulse and change direction to
try and confuse or throw them off. Another advantage the submarine had was that
they could react to the sonar pulse a bit earlier than the destroyer. This was
because the sonar pulse needed to return to the destroyer before they could get
direction and range data whereas the submarine could react as soon as they
heard the sound. It wasn't much of an advantage, however. At this range, the
echoes from the sonar pulse would be almost instantaneous.
Heimlich's captain ordered a slow turn to
the left to cover all directions. U-1215 was most certainly under the layer but
it would need to come up to get range data on the destroyer. He was determined
to prevent that.
U-1215
Werner had posted himself near the sonar
room, watched closely by the admiral. The operators were concentrating on their
instruments intently but made no reports. They were too far underneath the
layer to detect anything. Their course was unchanged as Werner thought it would
take them a bit farther from the destroyer. After several minutes, Werner
decided to take a peek above the layer to reacquire the Heimlich.
"Come up, slowly. Make your depth, 110
meters."
They had an idea of how deep the layer was
but this could change based on sea conditions. If they moved up too fast, they
could come out of the layer and be exposed before they could dive back into it.
Fischer reported that they were starting to
come out of the layer. Sonar quickly found Heimlich.
"Contact! Engine sounds aft. Making
turns for 5 knots...close...turning towards us." Werner gave a quick
command.
"Back down beneath the layer! Let's
hope he won't see us."
Fischer gave the order, bringing the
submarine down while Werner waited for the sonar operator's report. He had not
heard the active sonar but the sonar man had not mentioned it. He made a quick
decision.
"Fischer, we need to get far enough
away so we can fire our torpedoes. Go north, all ahead full. Stay under the
layer. After 30 minutes, slow to 1/3 and turn back. Let's try to reacquire him
and set up a firing solution."
S.S. HEIMLICH
As U-1215 sped north, Heimlich's captain
cursed his luck, mostly the lack of it. He'd lost contact with his quarry and
it was probably now getting ready to launch a torpedo at him. He didn't know
what kind of torpedoes U-1215 had but he assumed it was the same as the rest of
the submarine fleet. His sonar operator could hear those coming. He'd evaded
torpedoes before and he had some confidence he could outmaneuver them. Acoustic
torpedoes, however, were another matter. He'd never had any fired at him,
mostly because the other side didn't have them, at least none that he knew of.
He knew that submarines needed several
minutes to get a good firing solution and a target that constantly changes
course could disrupt those calculations. The normal method of searching for
submarines was to sail in a square while increasing the size of the square at
every revolution. That was a good method especially if there were two or more
destroyers to coordinate their movements. So he needed to run for several
minutes in one direction, change course and run for several more minutes. He'd
keep repeating that until he either reacquired his opponent or his opponent
fired a torpedo on him. If U-1215 fired a torpedo, Heimlich would have a direction
to go and continue his hunt for the elusive submarine.
U-1215
So far, the admiral had remained quiet,
staying out of the way and observing the actions of the crew and their captain.
Werner was learning how to use the capabilities of his new submarine. Other
submarines did not have the underwater speed or the stealth of U-1215. We will catch the Heimlich by surprise.
Thirty minutes later, U-1215 slowed to
one-third and turned around. They crept above the layer and immediately
obtained contact.
"Target to the south, bearing 174°.
Still pinging. Estimate range twelve kilometers."
Finally, thought Werner. They were going to
win this.
"Make tube one ready in all respects.
Open outer doors. Set torpedo course 174° and slow run up to ten kilometers.
Sonar, give me target's course."
"Getting it now, sir. Target course
seems to be 096°...no, wait! He's changing course."
So, Werner thought, Heimlich is using a tactic employed by most
surface vessels, change their course every now and then to throw off an enemy
submarine's firing solution. That might work with conventional torpedoes but
my torpedoes are anything but conventional.
"Target seems to have settled on
course 010°, captain. He's heading for us."
They were too far away for the destroyer's
active sonar to detect them but he was also a little too far for a sure strike.
The torpedoes had enough range to reach the Heimlich but if the destroyer
changed course before the torpedo acquired him, it may move out of the
torpedo's acoustic range. He came to a quick decision.
"Make tube 2 ready in all respects.
Set torpedo course to 164° and slow run up to 10 kilometers."
Werner waited for the series of commands to
be repeated before giving another one.
"Change tube 1 course to 184° and
maintain other settings."
Fischer, nodded his head. Werner was going
to fire two torpedoes, one to the left of the target and another one to the
right. That way, if the target changed direction either left or right, he was
going to have a torpedo coming toward him. Time to end this game.
"Open outer doors on tubes 1 and 2,"
Werner ordered.
"Open outer doors on tubes 1 and 2."
Orders are always repeated to ensure that orders were heard correctly. "Outer
doors on tubes 1 and 2 are open."
"Fire one!"
Tube one fired its weapon which immediately
turned to its preset course at 15 knots.
"Fire two!"
Having fired his weapons, Werner seemed to
relax a bit. "Now we wait. Fischer, estimated time to target?"
"Ten minutes, thirteen seconds,
Captain," Fischer replied. "The target is moving toward us at the
moment."
"Very well. Helm, right fifteen
degrees rudder, set course 310°."
Werner changed course to avoid getting too
near the Heimlich. With her active sonar operating, she might detect the
weapons though he might not know what they were. They were noiseless and Werner
hoped the Heimlich sonar operator would think they were large fish like a shark
or dolphin moving toward them. There was nothing else to do except to wait for
the next nine minutes.
S.S. HEIMLICH
Having just made a direction change,
Heimlich wasn't going to make another change for several minutes. The ASDIC
operator listened to the sounds of the returning sonar pulses. He had a fair
idea of the size of his target after the first contact was made so that was
what he was listening for. His ears picked up two returns but these were too
small to be the submarine. After two more pulses, he frowned. They were about
as big as sharks but these were faster, but not as fast as torpedoes. Dolphins?
Didn't dolphins swim in groups? These two were moving apart and were going to
pass him some distance to the left and right of the destroyer. Perhaps they
were playing a game.
The sonar operator suddenly realized that
he had made an assumption. He'd already set his mind into thinking these were
the swift swimming mammals of the sea. Might they be a new type of torpedo, a
slow one? But a slow torpedo would not be very effective. The Heimlich had a
maximum speed of 30 knots. These objects were moving at around 15 knots. At
fifteen knots, they might catch a slow freighter but only if they were launched
at close range. Typical torpedoes had a maximum range of only five kilometers.
Long range torpedoes? Did they sacrifice speed for range? All these thoughts
flashed through Heimlich's sonar operator in a split second. He decided to
alert his captain.
"Two unidentified objects in the
water, bearing 353° and 008°, moving at fifteen knots, Captain. They'll miss us
by about 600 meters on either side."
Heimlich's captain quickly picked up the
microphone. "Identify! Torpedoes?"
"They are not emitting any sounds,
Captain. All I can tell you is that they are about the same size as large
sharks or dolphins." A momentary pause. "Captain, these objects are
running straight. They must be a new type of silent running torpedoes."
Heimlich's captain made his own realization
in an instant.
"Helm, all ahead two thirds, make your
course 000°! Head right in between the torpedoes. That's where he is."
That accursed submarine was directly in
front of him. Not too far, for sure, and he had made an error in his firing
solution. The torpedoes were going to pass him harmlessly on either side.
"Captain, sonar. The torpedoes are
passing out of the ASDIC's detection angle. I'll lose them in a few
seconds."
"Ignore them, they're going to miss
us. Look for the submarine."
At that moment, Unit One's seeker head
switched on and began listening to the sea around it. There was a loud noise to
its left and it immediately turned towards it. Then, it increased its speed to
25 knots.
An acoustic torpedo had two sensors on
either side of its head. A louder sound on the left meant there was a noise
source in that direction. When the sound levels equalized, it meant the noise
source was directly ahead. Unit One's noise source was to its left, heading in
the opposite direction. As the torpedo turned, the noise source stayed to its
left. No matter, the torpedo was going to continue turning until the sound from
the two sensors equalized or until the sound disappeared. If the sound did
disappear, the torpedo was designed to turn around to re-acquire the target or
until it ran out of power.
Unit Two turned on its seeker head a few
seconds after Unit One. It turned to the right and slipped behind Unit One,
increasing speed to 25 knots. Both were now directly behind the Heimlich.
U-1215
"Target is heading this way, Captain.
Bearing 171°, fifteen knots. They don't have us yet but they will in about four
minutes."
"Increase speed to two thirds,
maintain course. Sonar, listen for the torpedoes making contact." Werner
didn't want to miss the sound of victory.
Fischer, shook his head. He'd have dropped
beneath the layer and changed direction but, then again, he wasn't in command.
S.S. HEIMLICH
"Prepare to fire the hedgehogs!"
Heimlich's captain could almost smell his quarry. The submarine couldn't move
faster than five to seven knots without draining its batteries in a short time.
He was sure he was now so close to his opponent that he should have already
detected him. Why was it taking so long for the sonar operator to make contact?
He needed to slow down and make a proper search.
"Slow to one-third."
As the Heimlich's speed dropped, the two
torpedoes gained ground even faster. As that point, Heimlich's sonar operator
found U-1215 and alerted his captain. With a cry of triumph, Heimlich's captain
ordered a course and speed change.
"Standby to fire the hedgehog!"
Heimlich's sonar operator frowned. He was
certain that the submarine had heard them approach and knew the ASDIC had found
them. Why hadn't they turned to evade? Then he remembered.
"Torpedoes inbound aft!"
Heimlich's captain face blanched as the
torpedo warning caused a heartburn. But the sudden grab of fear also galvanized
him to action.
"Left full rudder! All ahead
flank!"
Unit One sensed the target's sound shift to
the left and turned accordingly but it was a little too close and missed. Unit Two,
slightly behind, cut the corner and struck just forward of the screw. The
resulting boom was loud enough to cause the sonar operator to quickly clap his
headset off his head.
Damn it! Heimlich's captain, pounded his fist on the steel plotting table.
He'd lost the fight. He was shaking from rage as much as the adrenalin rush
from the torpedo warning. He ordered ahead one-third and commanded the sonar
operator to try to keep tracking the stealthy submarine. The fight was finished
but some pride in him caused him to try and tell that submarine commander that
he was not entirely invisible.
At that point, Unit One, which had turned
around and reacquired the Heimlich, struck the side of the destroyer causing
everyone to jump. Heimlich's captain, now even more enraged, cursed his
opponent out in the water beyond and stormed out of the bridge. The executive
officer watched the empty doorway for a few seconds, shook his head and ordered
half speed and return to port.
U-1215
"Sonar, what's he doing?"
"He's still at flank speed, Captain.
Bearing to the south on an easterly course. He's not...wait...he's slowing
down, turning away from us. Yes, he's changed course to the west and
maintaining around 12 knots."
Werner heaved a sigh of relief.
"We'll, I guess that's over. Engine's ahead two-thirds, set course for the
base."
The admiral stood up and shook Werner's
hand. "Excellent work, Captain Werner, excellent work. Congratulations to
you and the crew. I think this calls for a celebration when we get back to
base."
Amid the sounds of hurrahs and clapping of
shoulders, the admiral beckoned Werner to his stateroom. Werner let his men
celebrate for a few more seconds before giving a terse command.
"Silence! The reason why this
submarine is the quietest, is not because of its design. It's because of the
men who crew him. You may celebrate but do so without a sound. The enemy might
be lurking somewhere out there"
The admiral waited for him by the door to
the captain's stateroom. After both of them had entered and sat down, the
admiral began his critique.
"Well, Captain. That was a victory no
doubt. Instead of me giving my viewpoints on this exercise, I'd like to hear
your own analysis of the battle."
Werner, took a deep breath before speaking.
"Admiral, the beginning of the trial was not the usual way that a
submarine-destroyer duel begins. Heimlich was lying in wait and that is not
what destroyers normally do when they hunt submarines. If we had been allowed
to use our periscope, we might have found him from farther away and fired from
a safe distance. Of course, the rule of the trial was that we not use it."
"That it was, Captain. You could not
hear the Heimlich so you had no idea of where she was. You could have raised
your scope but without knowing where she was, you might have raised it close to
the destroyer and she could have detected you sooner. It might have been more
difficult for you to evade him then. Those are the fortunes of war, Captain. It
is useless to dwell on them."
"As you say, Admiral. The U-1215 is
certainly quiet but it is not undetectable. I knew that coming into this but I
was not sure how detectable until today. This is a valuable lesson for us. As
for our speed underwater, it is an advantage but only as long as the enemy
doesn't know about it. Heimlich was looking for us at our last position before
we made the sprint and that proved to be the opening we needed to get away and
obtain a firing solution."
The admiral nodded his head and waved at
Werner to continue.
"The torpedoes certainly work as
designed though Heimlich seems to have detected them with ASDIC. It might be
advantageous to fire the torpedoes beneath the layer so that they will remain
hidden until they become active. But that's only if the enemy is using their
ASDIC sonar. If they're using passive sonar, we can fire from any depth."
Again, the admiral nodded before making his
own observation.
"What you say are all valid, Captain.
There is one critique that I can give, however. After firing your torpedoes,
you changed direction but didn't dive. And when the Heimlich obviously detected
you, you continued on the same course and speed. Why is that, Captain? It's a
dangerous move to bait the enemy, especially knowing Heimlich's
reputation."
"Admiral, Heimlich was running
straight at the time of firing. By changing direction and allowing them so see
us, they would have to change direction as well and that would bring him into
one of the torpedoes. I had planned to head for the layer if he got too close
but I also wanted to hear the torpedo impact. I find it strange that he chose
to slow down when he did. That's what sealed the victory for us. I also find it
curious that he suddenly sped up. Did he detect the torpedoes behind him? I
find that hard to believe."
"As do I, Captain. I will have to
debrief Heimlich's captain when we get back to base. You were up against a
first rate vessel, Captain. And since he'd been with you through all the
trials, he probably had a good idea of your capabilities though he had been
told nothing. Congratulations again, Captain. You deserve it. You and the
crew."
"Thank you Admiral. Perhaps we can
start building these submarines now?" It was a question, not a statement.
"We still have one trial, Captain. If
it is successful, we will send the report to Donitz and he can inform the
Fuhrer. Hopefully, within the year, we can start construction of the first
group."
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