In a certain area of the East China Sea, more than 10 submarines and more than 10 surface ships are speeding underwater and on the sea surface in search formations, and there are anti-submarine helicopters in the air that have put down towed active sonar detection base arrays cruising, the roar of aircraft engines, and the sound of surface ships breaking waves are endless, and even submarines, which have always been very quiet, completely ignore noise, the biggest killer of submarines, and sail at full speed underwater.

The superiors gave a death order, and it was said at the very beginning, not acting, but that there was a real nuclear submarine hidden under water and ready to flee from Chinese waters. In order to prevent the nuclear submarine from sneaking out, the commander-in-chief dispatched by the Navy Command directly asked the aircraft with the fastest action to fly to the farthest place from the beginning to search back, and then let the slower submarine and surface ships retract in a circular search formation from all sides to the center point, so as to compress the activity space of the nuclear submarine as much as possible.

It was precisely because of this order that the nuclear submarine was frightened by the active sonar emission sources of the anti-submarine helicopter in front of it, which were almost scanned in rows, and could not escape directly, thus freeing up time and space for the relatively slow submarines and surface ships to search. However, because the range is too wide, the active sonar system is also relatively easy to expose signs of its own activity, so the nuclear submarine has not been able to be detected until the current location.

However, it is true that the nuclear submarine, which cannot move freely, has been compressed to move in space, and according to the sonar received, one or two non-stop search ships have begun to approach the direction of the nuclear submarine, but because the distance is still long, it cannot be detected for the time being.

The nuclear submarine, which was planning to turn its course again and avoid the search team, took the initiative to make some noises because Xia Yu wanted to snipe the three monitoring soldiers, which was the maintenance tool that fell to the ground. The sound of a small noise was transmitted through the hull of the submarine into the sea and in all directions, almost scaring everyone in the control tower to death, and at one o'clock there was a ship searching seven nautical miles away. Fortunately, the sound was not strong enough, or perhaps it was due to the influence of seawater media, which did not attract the attention of the search ship, so everyone in the nuclear submarine command tower couldn't help but breathe a sigh of relief.

But is it really not noticed? No. The sound made by the maintenance tool thrown by Xia Yu was actually captured by the sonar of a Type 039A conventionally powered submarine at that time, but because of the distance, coupled with the influence of seawater medium and other search ships and self-noise, the sonar of the 039A submarine only had a very weak sound signal, and the signal only appeared once and did not continue to appear, so it was ignored by the sonar crew.

The noise produced by the huge search team was much louder than the noise made by the pile of scattered maintenance tools thrown by Xia Yu, so it was not surprising that it was ignored, but the sonar of the 039A submarine still kept an eye on it, secretly remembering the direction from which the sound came, and planned to give a little more attention when he passed by again next time.

It didn't take long for the search team's missile destroyer 139 to take over the space after the 039A submarine search, and once again passed through this area, and it was at this time that several spaced continuous sound wave signals were captured, which was the sound of bullets hitting the bulkhead when Xia Yu and Ye Zi opened fire.

Although the sound signal is still weak and very unclear, the sonar of the 139 Ningbo missile destroyer is very concerned, and he reported his judgment to the captain at that time, and the sonar officer feels that there should be an unknown sound source in the direction of 8 o'clock, but he does not know the distance, and he is not sure whether there is really something in that direction.

The sonar's report attracted the attention of the captain, who had been searching this area for a long time and had found nothing, and even the submarine was required to send out active sonar, which proved that the matter should be very strict, and the captain did not dare to be careless, and immediately asked to search in the direction pointed out by the sonar officer with the Type 039A submarine that was turning around and meeting with him, and at the same time reported the relevant situation to his superiors.

Just as the two ships on the surface and under the water were moving in the direction from which the sound came, suddenly, the expressions on the faces of the destroyer sonar and the submarine sonar, who were engrossed in listening to the underwater movements, suddenly became very stern, and immediately attracted the attention of the commander.

"What's wrong?!" The captain of the Type 039A submarine had been paying attention to his sonar, and when he saw that the sonar's expression suddenly became stern, he immediately walked quickly to the sonar and glanced at the active sonar display screen, but he didn't find anything, so he asked directly.

"I just received a set of sound source signals, which should be Morse code." The sonar officer frowned, and at the same time, according to the signal that the ship had just arrived, while simulating the rhythm of the signal on his workbench, he said: "The signal is very vague, but it can be roughly distinguished, and the content of the code should be, Jiangsu, fly, rain...... Swift. Well, that's right, it should be the Jiangsu ship pilot Swift, but it was only received once, wait, and the signal! ”

The sonar man pressed the headset his ear, trying his best to hear the received sound wave information clearly, and the other people around him didn't even dare to take a breath of air, for fear of affecting the sonar's work, but the sonar was very dissatisfied with the various noise interference in the water, which made him not hear whether there was really a sound wave signal at all, so he said: "The active sonar and the propeller of the 139 ship are too noisy, I can't hear it clearly." ”

The same words were also said by the sonar officer of the 139 ship, almost only after a little thought, the top commanders of the two submarines immediately issued an order to turn off the active sonar, and the 139 ship directly stopped the propeller, just so that the sonar could hear the information from the sea more clearly.

When the active sonar of the two ships was turned off, and even the propeller noise was greatly reduced, the sound of the leaves tapping on the pipes with all his strength was quickly captured by the passive sonar systems of the 139 ship and the 039A submarine under the propagation of the seawater. "Dangdang dang dang", the sound signal without the slightest sense of rhythm came continuously, although it was not Morse code, and there was no text message contained in it, but for the sonar crews of the two ships, it was undoubtedly the most exciting thing, no matter what it was, but at least they now had a target to chase.