The Stirling engine is not liquid fuel burning, but through the helium stored in the tank, through cooling, compression, heat absorption, expansion into a cycle of power output, it does not need ignition, no knocking, the noise is quite low, almost like sailing with a battery.

At the same time, it does not directly drive the propeller at the tail, but drives a generator to supply power to the whole boat, and at the same time supplies power to the motor at the tail to propel the submarine forward.

At this time, the Stirling engine was spinning slowly, and the helium in the gas tank was constantly working until the helium was exhausted, and then it was no longer possible to sail like this.

"Accelerated to ten knots." Schupke gave the order.

When the Stirling engine was fully used, it could only reach a maximum speed of five knots, and now they have begun to use the power of the precious battery to speed it up.

This submarine is improved by adding a cabin to an ordinary submarine, retaining the same battery as an ordinary submarine, and can also use the power of the battery when needed, for silent navigation.

The five-bladed propeller at the tail has a faster rotational speed, but compared with the previous three-bladed propeller, the rotational speed has been greatly reduced, which makes it less noisy and not easy to detect.

They had been wandering around Sevastopol, no more than fifty nautical miles from the port, and now, at a speed of ten knots, they could reach the port in five hours, and it would be easiest to ambush them if they caught up with the other side and stopped in the port.

Underneath the conning tower, sonarists are carefully listening to the sounds of the sea.

In recent years, Germany's electronic technology has made rapid progress, thanks to the miniaturization brought by transistors, sonar machines have made great progress, and now, the sonar ball in the front of the bow is receiving clutter around it.

And listening in the clutter and spotting the other side's surface ships and submarines is the task of sonar crews.

Time passes little by little.

Shepke looked at his chart, which already had the first mate marked the trajectory, and according to his own voyage, there were still two hours to reach Sevastopol.

At this moment, suddenly, the sonar's brow furrowed, and in the midst of the noise, there was a completely different voice, high frequency, regular, rhythmic, and that was the noise of the propeller!

"Propeller noise was found, about twenty nautical miles away." The sonar officer said.

Twenty nautical miles away, that means the other party has begun to leave the port! Schupke felt his adrenaline rush and the wet smell of diesel fuel in the submarine made him feel so fresh.

"Ascend to periscope depth." Shepke shouted.

Just now they had been sailing at a depth of about fifty meters, and now, the huge submarine began to slowly raise its head, and at the same time, on the conning tower, a periscope slowly rose.

If it were any other submarine, they would have to raise the snorkel and charge the battery for a short time, but for now, they just need to raise the periscope.

At a depth of ten meters, the submarine leveled, and Schupke pushed the periscope in front of him, putting his eyes on it.

The sonar of this era was not advanced enough to provide torpedoes with firing elements, and the attack on enemy warships still relied on periscopes, and at the same time, periscopes were also needed to confirm targets.

When Schepke fixed his eyes on the periscope, the sea was sparkling, and the quiet moonlight sprinkled all over the sea, and the surroundings looked very clear.

Well, the visual distance of being able to see the outline of an enemy warship is at least three nautical miles, which is enough to identify the target.

Pushing the periscope, Schupke's feet slowly turned, and at the same time, the field of vision inside the periscope also rotated, and suddenly, he was happy: "Right rudder one, full speed!" ”

On the surface of the sea, you can see the flickering lights, which are the navigation lights turned on when the ship is sailing!

I really didn't expect that at such a time, the Soviets would actually turn on their navigation lights when they set sail in battle.

Receiving the order to move forward at full speed, the sailor turned the operating stick in front of him to the position of advancing five, and with his toggle, the lights of the whole boat suddenly dimmed.

They still didn't turn on the diesel, and sailed entirely on their own battery power plus the power of the Stirling engine, with the tail propeller spinning at an accelerated pace, pushing the water.

In the periscope, the target is getting closer and closer.

The other party is sailing at high speed, in this case, it is impossible for them to detect the submarine underwater, but just in case, the noisiest diesel engine is still not started, at maximum speed, their power will be quickly consumed, and by the time they get there, there may be half of the power left.

If it is an ordinary submarine, no captain dares to do this, after all, for submarines, the most precious thing is electricity, if more than half of the electricity is consumed, then you have to think about charging at any time.

But now the AIP submarines are not needed, they can use their Stirling engines underwater at any time, they do not have to risk rising to the snorkel state, if they really encounter a large number of anti-submarine operations of the enemy, they will sit quietly on the bottom of the sea, wait for the other party to leave, and then say, they can hold on for a week, they will have more perseverance than anyone.

Now the U-100 has no scruples, they are sailing at a depth of ten meters under water, at high speed, and the distance from the other side is getting closer and closer.

"Left rudder one, stop, ready to enter the ambush position." Schupke continued to give orders.

If the submarine wants to attack surface ships, it must pay attention to strategy, for example, the torpedoes used by submarines now, the main ones are direct torpedoes, in this case, it is necessary to hit the maximum projection area to be possible, that is, to hit the side of the opponent.

Therefore, if the submarine wants to attack, it must occupy the attack position in advance and set up an ambush on the opponent's expected shipping lane.

Now, the propeller at the tail of the submarine stopped rotating, and suddenly the entire hull began to slow down, and the rudder surface moved, and the submarine slowly turned its nearly 2,000-ton body to occupy the preset attack position.

Shepke's eyes kept staring at the periscope, and the warship that came out gradually revealed its outline, and after seeing it clearly in the moonlight, Schupke suddenly became excited.

Whatever you want, the only battleship in the Black Sea Fleet came!

That battleship looked so magnificent, and at the same time, the most exciting thing was that it was actually a lone one, and there was not even a convoy nearby.

"There is constant noise, and at a distance of ten nautical miles, a large number of warships have been dispatched." The sonar officer said.