Scattered snowflakes drifted down on the dark sea, and it was already dark. As this cold air from the Arctic Ocean continues to move south, the climate in the North Atlantic becomes unpredictable. The escort warship and the entire flotilla began their routine anti-submarine emergency turn again, the bow of the ship cut open the water, and the waves crashed against the hull of the ship to make a rhythmic "whoosh" sound.

In the North Atlantic, an unattacked voyage was a luxury for every British sailor, who had lost 269 merchant ships and more than 1.4 million tons of cargo in just four months since the fall of France. Seventy percent of these merchant ships were sunk by German submarines.

However, with the establishment of an increasingly strict escort system and the widespread application of new anti-submarine technologies such as sonar, anti-submarine patrol aircraft, and new depth charges, it became more and more difficult for German submarines to find a good opportunity to attack.

As we all know, during the last world war, the submarine force, as a sharp weapon of the German Navy, dealt a great blow to the Entente bloc, and became an underwater demon that terrified the merchant ships of various countries. The German Navy has always been at the world's leading level in submarine technology, and although the development of military technology has been somewhat slow in the more than 20 years since the end of the war, German submarines are still far ahead of other countries in the world in terms of comprehensive performance.

However, as control of the Strait of Gibraltar fell into the hands of the Axis bloc, the surface warship forces of Germany, Austria, and Italy gradually began to penetrate deep into the Atlantic Ocean to carry out blockade and dismantling operations, and the combat mission of the German submarine forces was quietly changing, from the main force of the past attack to the vanguard of reconnaissance and monitoring of the enemy's movements.

Since the beginning of November, the German Submarine Command has informed the boats of the Admiralty's latest operational regulations: not to risk attacking the enemy's escorted convoy under unripe conditions, but to monitor the target and report the information to the Admiralty Headquarters at the first opportunity.

As a result, from November, the "record" of the German submarine forces showed a noticeable decline, and of course, the advantage of this was that the losses of the submarine forces were also minimized.

"Sir, we've reached Target 152!" About 30 nautical miles in front of the British transport fleet numbered HZ-11, the German Navy submarine U48, which was on a combat cruise mission, quietly surfaced in the night.

The German Navy built a total of nearly 500 submarines of various types during World War I, and only retained more than 80 U-boats and 50 UB-48-class submarines after the war. Before the war, the German Navy built only 5 types of 22 new submarines of experimental nature, again numbered from U-1. In fact, the U48 submarine was one of the first 60 UVI.C/39 ocean-going attack submarines built by the German Navy in batches after the outbreak of the war, and was similar in tonnage and performance to the UVII.D/40 submarine built for China, except that this type of submarine was equipped with a 75mm deck gun and was not equipped with a rocket launcher.

Since the submarine has set sail, the navigator will mark the route of the submarine and the time of arrival at the specific location on the chart according to the speed and course of the submarine. It is a common practice for navies of all countries to numerically number each sea area on the chart within a 30×30 nautical mile grid to facilitate communication. These numbers are changed and changed at different times, and the Admiralty will provide each ship with three charts with the latest sea area number for use in liaison before the ship sets sail.

"Move forward at one-third speed!" When the captain of the ship, Major Schultz, who was on the bridge, heard the report and gave an order to the boat, "The radar is on, pay attention to the western sea!" ”

Due to the interference of the cold snap, the sea surface is rough, and from time to time the waves will split their heads and cover their faces and pour on the small bridge of the submarine. The crew on duty on the bridge was wrapped in wet raincoats and vigilantly searched the nearby sea. In this day and age, radar and sonar are actually much farther than the eyes of the crew, but most captains still prefer to trust the human eye.

It was dark and dreary in the distance, and there was no movement except the monotonous sound of the waves.

Since the invention of the underwater snorkel, submarines have theoretically not surfaced from time to time to recharge batteries, but only need to remain at periscope depth to stay underwater. But in reality, the underwater snorkel sometimes malfunctions, and the crew prefers to let the submarine float at night to get some fresh air.

Thanks to the advent of anti-submarine patrol aircraft and airborne radars, the enemy's anti-submarine range has increased considerably. Now, except for routine cruises in the open ocean where the enemy is not visible at all, submarine commanders generally do not surface at all during the day, unless there is some malfunction.

Major Schultz watched from the bridge for a while, and seeing that there was no movement, he slipped from the bridge to the compartment below. After taking off his raincoat and cover, he sat down on a chair in the dining room with his shirt on and drank hot coffee.

"Sir, we won't miss them, will we?" The nautical staff officer rummaged through a telegram in his hand and sat down opposite the captain. He was referring to the British HZ-11 transport group, where the Admiralty has mobilized at least six submarines to track the fleet.

"Probably not, we have four submarines in the vicinity, so a large fleet can't escape all sonar listening unless they return." Schultz said calmly that there would inevitably be some accidents with such a large fleet, and it was not uncommon for the voyage to be missing by a day or two. ”

"Shall we attack first?"

"No, you need to report it upwards first."

At this time, in the dimly lit sonar room, the non-commissioned officer on duty of the submarine wearing headphones has been paying attention to the situation in the sea.

"Report, 220 azimuth found high-speed propeller! There should be more than one! Just as Schultz was about to return to the captain's quarters, a loud report from a sonar soldier came over the loudspeaker in front of the periscope.

"Whoa, whoa......" The submariner's alarm sounded.

"Prepare to dive!" Schultz ran back to the captain's command position and said loudly.

The submarine began to dive, and through the thin pressure-resistant shell, the sound of water filling the tank could be heard, and the hull of the boat creaked and creaked as it dived rapidly, which was terrifying. After a while, everything outside suddenly fell silent, and the submarine had completely sunk into the water.

"Periscope length, raise the periscope! Report the situation of each part! Schultz was giving orders.

"Yes sir, 13 meters deep! One qiē is normal. "There was a report from the pressure control room in the loudspeaker, followed by a report from the power compartment, the torpedo compartment and other parts, and it was normal.

The crew at the bow and stern of the boat stared at the depth gauge by the large steering wheel, the third Pratt stood next to the trim adjuster, and the sound of an echo rangefinder coming from the sonar room came from the loudspeaker, and the sound of many propellers mixed together.

"Good. Now, raise one more meter! Scholz's voice was resolute, the waves on the surface of the sea were so strong that from time to time they would flood the periscope. The periscope in front of him was quietly rising, and Schultz was manipulating the periscope to rotate and search the sea. After a while, his hand stopped, "Good boy, there are more than a hundred boats." Not good, dive fast! ”

Schultz noticed that suddenly a destroyer left the formation and was approaching in the direction where they were. R1152