A certain year, a certain month, a certain day.
A certain sea region.
200 meters below the surface of the ocean.
Dusk Zone.
At this depth, the sunlight was as dark as dusk.
Looking down, there was a pitch-black abyss below.
Looking up, it was like the brief period of blue sky after the sun had set before the sky turned completely dark.
What was different from the real sky was that there were no tired birds returning to the forest. Occasionally, there would be a streamlined shadow swimming quickly overhead. It was a large shark in the shallow waters.
At least half of the marine life could not reach this depth, but in the faint light, there were still some things quietly moving.
Whoosh —
A shadow swam past at a very fast speed, its body reflecting a dim silver light. Few things could cruise at this speed in the sea.
It was an adult swordfish with a body length of nearly two meters. It had a long jaw shaped like a fencing sword, and it swam tyrannically and recklessly. In this depth of the ocean, it relied on its superior speed to have almost no natural enemies other than sharks.
Its eyes were very large, the size of tennis balls, and distributed a large number of light-sensitive cells. If it wanted to hunt in this level of light, it would be impossible if its body did not have some special characteristics.
It had a long, sharp jaw, keen vision, a body that weighed hundreds of kilograms, and a sprinting speed of more than 100 kilometers per hour. This gave it the capital to be proud of. When it went crazy, it was as terrifying as a harpoon. It even had the reputation of "piercing through wooden planks" …
This swordfish had bad luck today. It had not found anything to eat, and hunger had turned it into a grumpy old brother. It wanted to find an eyesore to sleep with for a day, anything would do.
In front of its high-speed swimming route, a large black fellow suddenly appeared. That slow swimming speed made it seven to eight out of ten to be a whale.
Even the fastest whale could not eat the exhaust of the swordfish, so it was very confident in provoking it.
Perhaps it was because its speed was too fast, so fast that it didn't even see what the other party was before it rushed over. When it got close, it realized that something was wrong, and hurriedly twisted its strong muscles to make a sharp turn, narrowly avoiding the collision with the other party.
What was going on? Why was this fellow's body so long? It was much longer than the largest whale it had ever seen. It had a perfectly round head, a "dorsal fin" that was as thick as a reef, a pectoral fin so small that it was almost invisible, and a tail fin that rotated periodically to stir the seawater. It did not look like a stupid whale at all … Most importantly, its skin seemed to be much tougher than a wooden plank.
Forget it, I'll just find a pushover.
With a flick of its tail, it angrily swam away and disappeared into the dim light.
The nuclear submarine, which was mistaken for a whale by the swordfish, cruised silently underwater at a speed of six knots. Along the way, it passed under dozens of different types of ships, including fishing boats, cargo ships, oil tankers, private yachts, and even took the risk of coming into close contact with a warship. Fortunately, it was not discovered by any ship.
It dragged a long "tail" behind it, longer than any tail in nature, with a total length of almost one kilometer, including an 800-meter-long towing cable with a diameter of less than one centimeter, and a sonar array that was more than 100 meters long and composed of thousands of hydrophones.
The towed sonar array worked at wavelengths below 3,000 Hz, and the lowest effective frequency was an extremely low frequency of 10 to 20 Hz. Through the deep-sea sound channel and the convergence area effect, the furthest detection distance reached 180 kilometers, and it could even obtain intelligence and topographic features outside the territorial sea line of other countries.
In the narrow sonar room.
Sonar Operator No. 1, wearing a military uniform and headphones, stared intently at the screen in front of him, looking for traces of the enemy nuclear submarine.
All sounds from within a range of 180 kilometers were captured by the sonar array, and after being output amplified, they were transmitted to Sonar Operator No. 1's headphones, and the waveform was displayed on the screen in front of him through the tuning indicator.
Sonar Operator No. 2, sitting next to him, was responsible for the operation of the sonar at the bow and the echo detector.
Sonar Operator No. 1 periodically switched the buttons and adjusted the filter, sometimes increasing the low frequency, and sometimes increasing the high frequency, in case there was an enemy submarine quietly approaching in the sound and shadow area.
The sparse stubble on the side of his lips proved that he was very young, but he had been on duty in this submarine for a year. He was not a recruit who panicked when something happened, which could be seen from his calm and experienced expression.
A variety of sounds alternated in the headphones, and he knew most of them like the back of his hand. If not for that, he would not have been qualified to get off the boat and become the eyes and ears of the submarine.
The nuclear submarine was very quiet, and the noise it made was very small. Its operation process was far less noisy than that of a diesel submarine.
He could distinguish the crisp crackling sound of the shrimp's bouncing body, the sharp chirping of the dolphin, the unpleasant sound of the golden drum fish, and the croaking sound of the yellow croaker, which was like the croaking of a frog … This kind of unimaginable keen insight in the imagination of others was just a part of his work and training for him. He did not have extraordinary hearing, but after listening to it many times, he remembered it — there was no other reason than that it was familiar to him.
Suddenly, his straight eyebrows moved slightly, and he heard an unfamiliar sound in his ears, which disappeared in a flash.
He did not let go of any abnormalities. The waveform on the screen just now still remained in his memory. He adjusted the button according to his intuition, turned on the low-pass filter, and increased the low frequency.
The sound came back again.
His eyes moved quickly, glanced at the frequency slightly, and found that the range of this sound was between 45 and 50 Hz.
Was it a whale?
The submarine often encountered whales, and he was familiar with all kinds of whale sounds. In his memory, there were indeed some whales that could make sounds in this frequency range, but the specific sound was different from what he had just heard.
"Number 2, please confirm the position. Frequency band 45-50," he said.
Since the towed sonar was a straight line, it was difficult to determine whether the source of the sound was from the port or the starboard. It required the assistance of other sonars, or the submarine's maneuvering direction to confirm, but the submarine in a cruising state could not change direction just because of a little abnormality, so he could only choose the former.
"Understood." Sonar Operator No. 2 answered crisply and adjusted the passive sonar at the bow to a low frequency gain of 45 to 50 Hz.
Sonar Operator No. 2, who was also young, stared and listened for a while, then said, "Position 090, identity unknown."
"Roger!" Sonar Operator No. 1 said.
"Sir!" He took off his headset and called for the officer on duty.
"What's the matter?"
The officer on duty immediately walked over quickly, and he arrived as soon as he called. He was much older than Sonar Operator No. 1, and he was mature and experienced in the truest sense. The wrinkles at the corner of his eyes and the military rank on his shoulder also proved this.
"Suspicious contact, position 090, sound like a whale," Sonar Operator No. 1 reported concisely.
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