The idea that if all six warships were involved in the alert rotation, then each warship only needed to turn on the passive sonar to be enough to do a drop of water, but now only the K14 frigate responded to Finch's plan.

Therefore, Finch can only choose to exchange space for time, turn on active sonar to expand the search range, and buy more reaction time for the fleet. Of course, this approach also has its side effects, that is, the hydroacoustic signal that travels rapidly along the sea water will be captured by the target as well as the target.

For example, at this time, the passive sonar of a Type II U boat cruising nearby picked up the underwater acoustic signal from the K11.

The sonar crew of the U-23 submarine was drowsy from nearly midnight, but a strange sound from the headphones woke him up instantly.

The sound was so subtle that it was caught in the noise of submarines and the noise of the ocean, and it would have been impossible for ordinary people to detect it, but as a sonar soldier, he was different from ordinary people, he was professionally trained.

"Mr. Captain! There are suspicious voices! He listened for a while and immediately reported to the captain of the boat, Otto Krezimer.

"Huh?" Hearing this, Krezimmer stood up from the captain's seat, walked over to the sonar soldier, took the headphones, and listened carefully.

Soon, he heard from the crowd of voices what the sonar soldier called "weird sounds".

The sound is very similar to that of a whale, very dull, "woo-woo-woo".

"Mr. Captain, this voice looks like a whale." The sonar soldier scratched his head and said, "There are often megalodons in this area, and the last time the 'cows' refueled us, one of the sailors on the 'cows' told me that they had encountered a group of megalodons. ”

"Megalodon?" Krezimmer thought for a moment, then shook his head flatly, "No, it's not a megalodon, it's a social animal, and several of them often move together, and this sound comes from one thing from beginning to end, and it is repeated again and again in the form of pulses. ”

"Then what do you mean ......"

"This sound comes from the Navy's low-frequency active sonar!" Krezimer was determined.

"Navigator!" He put down his headphones and called out to one of the sergeants in charge not far away.

"I'm here, sir."

"Take a look at the maritime bulletin from the headquarters and check if there are any of our surface ships in the vicinity." Krezimmer ordered.

When the navigator heard this, he immediately lowered his head to look through the information, and after going through it several times, he replied: "Sir, there is." There are several surface ships in the waters near us, but they are all large torpedo boats and the like. ”

"That is, we do not have surface ships equipped with active sonar in the vicinity?"

"Yes, according to the briefing, no!" The navigator replied.

"Then this ship is an Englishman or a Frenchman." Krezimmer grinned, "Mechanical, lift the radio silence and turn on the radio to inform the surrounding friendly ships." The whole boat is first-class combat readiness! ”

Under the command of Krezimer, the whole submarine began to operate in an orderly manner, all the sailors who were resting were called, and in the front torpedo compartment, three 24-inch (610mm) heavy torpedoes were pushed into the torpedo tubes by the officers and men to standby, and the other combat positions also quickly entered the combat state from the normal state.

"Sir! U-24, U-27, and U-30 indicated that they were on their way to participate in the attack. The electromechanical crew quickly got an answer from other submarines around.

"Good." Krezimmer nodded, "Turn on the active sonar and locate their specific location and distance." ”

"Yes! Turn on active sonar. ”

As the sonar soldier flipped the switch on active sonar, a sonic wave that was sharper than the British sonar was transmitted from the active sonar array of the U-23 submarine.

Unlike the low-frequency sonar equipped with the K11 frigate, the German U-boat is equipped with medium-frequency sonar, which is specially requested by Lyon, because it takes into account the characteristics of long-range detection of low-frequency sonar and accurate detection of high-frequency sonar.

Soon, the medium-frequency sound waves that flew through the sea crashed into the hull of the J11 minesweeper, which was closest to the U-23, and then reflected back into the hydrophones of the U-23 submarine.

The sonar soldier quickly located the position and course of the target according to the reflected speed and azimuth of the sound waves, and then immediately turned off the active sonar, turned around and reported to Krezimer: "Sir! The enemy ship was located due south and headed northwest at a speed of 10 knots, only 6 nautical miles from us. ”

"Keep up! Keep your distance and be careful not to be caught by them! Krezimmer patted the second officer at the helm on the shoulder.

The second officer nodded, and then operated the submarine to the sonar man's reported position.

At the same time, on the K11 frigate.

Sergeant Burris was the sonar officer of the frigate K11, and he was supposed to be resting now in the original order of duty, but because of Captain Finch's impromptu decision, he had to get up from his sleep, put on his headphones and turn on the sonar, ready to be "baptized" by those boring noises and the same "whine" to his ears.

But this time, it wasn't long after he turned on the active sonar that he heard an unusual echo.

The reverberation was faint, but it was there, which suggests that the active sonar captured something, but at a distance from the fleet.

After thinking about it, he reported the situation to Captain Finch.

"Captain, maybe you should come and listen, the sonar has picked up something." He took off his headphones and said to Finch.

"Caught something?" Finch's face was serious, "What's that?" German submarines? ”

"I'm not sure." Burris shook his head and said, "The fleet is so noisy that it's hard for me to tell if it's a submarine or a German submarine...... Wait a minute! Captain, the hydrophone seems to have picked up something else. ”

"Fish?"

"No, it shouldn't be...... Damn, it's gone again! ”

"Whatever it is, I think those idiot captains should be in good spirits." Finch turned to the signal soldier and ordered, "Use the light signal...... No, turn on the radio! Report this to the other ships! Tell them that we could be attacked by German submarines and that we must immediately change course! ”

"Yes!"

Soon, the reply from the K27 frigate arrived: "Captain Finch, I think you may really be overthinking, there are too many things in the sea that can reflect your sound waves." Also, German aircraft and surface ships pose a greater threat to us than German submarines, and your disruption of radio silence is likely to attract them! ”

"These idiots!" Looking at the contents of the telegram in his hand, Finch angrily punched the table.

"So what are we going to do?" The officers and men in the bridge all looked at Finch.

"Leave them alone! Let's get off the line and get out of here immediately! Finch was resolute.

The frigate K11, on the orders of Finch, began to change course and turn to the southeast.

It has to be said that Finch's decision was very correct, because the U-24, U-27, and U-30 submarines had stopped in front of the fleet after receiving information from the U-23, and the turn of the K11 frigate allowed it to successfully avoid this trap.