Excerpts from U-1215's Trial Orders
U-1215 Trial 1 - Surface Running at Various Speeds
Trials will be conducted after dark starting at 2100H, local time. Upon exiting the u-boat pen, you will proceed to conduct surface speed runs at different settings thus:
Ahead Slow
Ahead 1/3
Ahead 2/3
Ahead Full
Ahead Flank
You will also conduct trials in reverse engine configurations.
You will run the trials in a racetrack oval ten kilometers long, reversing your course at running speed.
During these trials, you will be assisted by the destroyer Heimlich, who will provide protection and warning in case another vessel approaches. Under no circumstances are you to allow U-1215 to be seen by anyone, friend or foe. If necessary, you may dive the boat to avoid detection but no deeper than periscope depth.
The new moon was two days before which meant it would be dark during the trials. The weather was also cooperating though clouds covered most of the sky. The secret pen was situated a long way from the main submarine base in Lorient but that did not discount the possibility that a friendly would blunder onto them.
The boat was pulled away from the pier by lines on the opposite pier. Her bow was aimed at the entrance which was still closed. The massive granite rock had been hollowed out to make the sub pen. The part of the rock that faced the ocean had been cut to form doors that were hydraulically-operated. The outside face of the doors were made of the same granite and finely constructed so that no one could see the seams unless the observer was very close.
The guards checked the surrounding area as well as the sea before reporting that the immediate area was clear. The Heimlich was already 20 kilometers out to sea looking out for any vessels that may stray into the trial area. She gave the all clear signal as well.
Werner, Fischer, Meyer and four other men were on the bridge waiting for those signals that would allow them to open the doors of the pen. The deck was already clear of men, all external hatches closed except for the one on the bridge. When the all clear signal was given, Werner ordered the doors opened.
All the lights in the cavern were extinguished and the huge doors began to open. For such large doors, they hardly made any sound as they swung open. The doors extended down into the water which made it necessary to have them open very slowly to minimize the creation of waves. Werner kept himself from tapping his feet with impatience as he waited for the doors to fully open.
As soon as the doors had stopped moving, he gave the order to Fischer. "Ahead slow, Mr. Fischer." Fischer repeated the order word for word before giving the order down to the control room.
Almost imperceptibly, the large submarine began to move. Werner looked aft to check if the water was being churned only to remember that there was no propeller to do the churning. He did see waves appear behind the tail and the boat began to pull away faster. So, he thought, the propulsion system works.
U-1215 passed through the doors and into the open ocean, her sharp, chisel-like bow cleaving the water easily, gaining speed gradually. When the submarine had moved far enough, the sea doors of the pen began to close again. Soon, no one could tell that the granite face was anything but a massive rock by the sea.
When the speed had remained steady for a few minutes, Werner checked the speed on the indicator on the bridge. It read three knots. He ordered a yeoman to record the speed in the trial logbook. They would take several readings at regular intervals to establish the actual speeds at each engine setting.
The propulsion system had a water intake at each side of the boat near the tail just under the waterline. Instead of a tube, like Schmitt's demonstration jig, they were slots which fed seawater into the magnetic propulsion device before being expulsed out the tail. The entire tail was fully submerged so that no air would enter the tube and cause "sputtering," a term they came up with to describe the sudden surging and loss of propulsion when the air bubbles interrupted the electric current through the water. It also caused power surges in the sub's electrical systems which could cause fuses to blow. The system was most efficient and safe to use underwater but since they also had to run on the surface, it was important to find any problems and fix them by either redesigning, making adjustments, or changing procedures.
Werner couldn't order a faster speed as yet. They had to find out how the vessel handled at every speed setting. It's going to take forever to reach the entrance to the small bay, Werner thought. The bay might be too small to turn the boat around in a circle. Soon, however, they left the bay and entered deeper waters. Sea conditions were light with small, half-meter waves that didn't cause the large submarine any problems. Werner waited until they were about five kilometers away from shore before ordering a slow turn to port. The submarine made the turn without incident or difficulty. After turning a complete circle, they continued for another five kilometers before Werner ordered a tighter turn. For the next hour or so, they kept making turns and recording the boat's response and turning radius.
SS Heimlich kept watching the surrounding area looking for friend or foe. She was a captured French destroyer, fitted with an ASDIC sonar that was salvaged from a captured British destroyer. She was fast and crewed by a select group of naval personnel. Often tapped to conduct submarine evasion tactics with u-boats, she was as experienced as or better than a lot of the ASDIC-equipped Allied ships. Her role tonight was to just watch the waters around the trial area and warn away any vessels that might see U-1215. She, herself, maintained a 15 kilometer distance from the trial area.
Around 0300H, Werner ordered the U-1215 to head back to the secret sub pen at 10 knots. They had run racetrack ovals all night and it was time to return to base. U-boats returning from patrol usually timed their arrival during the daytime. The war made it necessary to keep the main u-boat base as well as the surrounding areas dark at night. With no visual navigation aids available, u-boats usually waited out at sea until it became light enough to make their approach. Werner had to return to base before they moved in to avoid being seen.
The tests were not complete, however. They had to return the next night to run the remaining surface tests and this was done without problems as well. Werner learned that the submarine was not very fast or maneuverable on the surface. At full speed, they clocked at only 15 knots, going up to 18 knots at flank speed. Wave action, however, caused sputtering especially at faster speeds. If they had to surface in swells of over three meters, their speed would be cut severely and risk popping fuses. Replacing fuses was quick and easy but no one wanted any complications in case they needed the speed. Werner couldn't wait for the submerged tests so he could find out how U-1215 performed in her element, underwater.
They encountered no intruders though Werner knew it was only a matter of time before someone strayed into their trials. He had no orders except to dive and be silent but he didn't know if SS Heimlich had a different set of orders. Was he authorized to shoot? Werner had no contact with the Heimlich's commander, both of them just doing their own thing, not minding the other. The admiral had told him that the destroyer had orders to guard U-1215 and assist in some of her trials though the crew were informed that they were just helping to train ordinary u-boats in evasion tactics. Werner was not to allow the destroyer to see the secret u-boat or to communicate with her.
***
Underwater
Werner watched as the sub pen crew turned U-1215 around so she faced the sea doors. The pen was large enough to turn U-1215 around completely though this was done with electric winches instead of tugs. She was being readied to run her underwater trials tonight. The timing was good since the moon would be one day short of first quarter. With her hull painted black, it would be difficult to see U-1215 when she was on the surface.
The water depth at the entrance to the secret sub pen was such that they could exit the pen partially submerged if the weather was good. Werner decided to do this as it improved the handling and the speed of the sub. It meant that the bridge crew would get more wet than usual but better for them to experience these things on occasion.
They had to travel at least 10 kilometers before they can safely submerge to at least periscope depth but the actual trial area was 100 kilometers away. The depth there was more than 100 meters which was enough for their speed trials. At 10 knots, it would take them a little more than 5 hours to get there and they were to conduct the trials continually until 2300H the next night when they were to head back to the secret sub pen. The SS Heimlich was again going to accompany them though both would not see each other. The sonar operators in both vessels planned to practice detecting each other though the destroyer would have a harder time detecting the submarine.
While the tests were proceeding, U-1215 had occasion to hear a few of their fellow u-boats while they transited the area. They avoided contact with these submarines as ordered but Heimlich relished the opportunity to practice her detection and pursuit tactics. The other u-boats were aware of the Heimlich's presence and did their best to avoid detection and evade the expert sub hunter. Werner was going to have his opportunity to practice attack and evasion tactics against the Heimlich but not today.
The trials went well except for a problem with one of the kitchen's stoves. A minor inconvenience that Werner took hardly any notice. Their maximum underwater speed at 100 meters was 21 knots.
Sonar Practice
The design intent for the U-1215 was that she not use her periscope if possible. Other than being spotted on the surface, the main method for spotting submarines was by seeing the periscope "feather," the white-colored wake the thin mast makes as it plows through the water. Werner's task was to try and see if they could reliably target and hit any ship with just the sonar. It wasn't impossible really, in fact, lots of u-boat commanders were doing that right now, even without a U-1215. The difference was that they did it only when they couldn't use their periscopes for one reason or another. Sonar was good for finding direction to a sound source but it wasn't easy to use for determining the range or for identifying ships. The advent of the acoustic torpedo simplified targeting but the sub commander still needed to know if a target was within range before he could fire his weapons.
U-1215 had several sonar sensors along each side of the conning tower. Essentially, the conning tower was a big head with an ears on each side. It enabled one of the sonar operators to determine the direction to a sound much like a human normally does with his pair of ears. The system also produced a trace on a paper recorder that focused on the loudest sound it hears. From the trace, he could tell the bearing to the sound relative to the sub's heading and he also had a historical trend of the sound's movement. There were two of these recorders in the room. One was working while the other was loaded with a large roll of paper, ready to take over when the other one ran out of paper. They had enough paper to last seven weeks at sea.
There was another display in the sonar room that looked like a radar scope. The sub had a separate sensor that the operator could point in any direction he wanted. The scope would show where he was pointing it and show the approximate distance by a blip on the scope. The system worked out the distance by the loudness of the sound. The louder the sound, the closer the blip was to the center of the scope. By careful adjustments, the operator could give a fair estimate of the distance to the sound source.
To test all this, U-1215 was conducting a trial with two vessels. One was the SS Heimlich and the other a small merchant vessel. The two vessels were to sail close to each other and then farther apart. They sailed in opposite directions and at right angles to each other. The sonar operators in U-1215 had to determine which vessel was which and their positions relative to each other and to U-1215. The plotting team on U-1215 traced their movements on the chart table and would later compare them with the ship's own charts after returning to the base. At the same time, Heimlich tried to detect and track them without going after them. Going after them was another test.
It was more of an exercise than a test really. They did this continuously for two days. At the end of it, they discovered that U-1215 had tracked and plotted both ship's movements with fair accuracy. The sonar sensors and the target tracking equipment were working perfectly. The admiral was very pleased at that. It meant, at least, that the new sub could find their targets. He was even more pleased to learn that Heimlich had not even heard the submarine. They had heard two other u-boats but not the silent U-1215.
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