Monday, November 9, 2015


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.

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.

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.

"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.

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 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.

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°."

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°"

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.

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."

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.

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°, 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.

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.

"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.

"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.

"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."

Werner smiled and received the admiral's congratulatory hand.

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