Chapter 789 Hawaiian Islands (10)

The German fleet anchored in the waters of Oahu, the communicator reported to Commander Hermann. "Commander, our destroyer found a suspicious signal 50 kilometers northeast of the sea, suspected to be an enemy submarine."

"These idiots, are they here to die?" Commander Hermann sneered and ordered casually. "Sink them!" Who else could appear here except the US submarine?

The adjutant on the side said. "It seems to be a US submarine supporting Oahu, maybe it is to send them fresh water purification equipment. But it is just right to use it to try our latest sonar system."

The collision of the luxury liner "Titanic" with an iceberg in 1912 and the outbreak of World War I in 1914 greatly promoted the research and development of civilian and military sonar. The first anti-submarine sonar was introduced in World War I, but due to the imperfections in theory and technology at that time, the performance of this hydroacoustic echolocation system was very unreliable, so it had not yet made any contribution to dealing with the threat of German U-boats.

The research on sonar did not end with the end of World War I. Until 1935, Germany, Britain and the United States developed several more practical sonars. In 1938, sonar equipment began to be mass-produced in the United States. In the original World War II, almost all military ships were equipped with sonar systems and played a very important role in naval battles. At that time, the warring parties lost more than a thousand submarines, most of which were discovered by sonar.

"Report, the enemy's destroyer is approaching at high speed!" In the underwater US submarine, the submarine sonar operator listened quietly for a few seconds and immediately reported to Captain Thomas on the side. Just now they also found the German destroyer patrolling in the distance. Although they dived in time, they were obviously discovered by the other side.

"Dive to 30 meters and reduce the speed to 3 knots! Reduce noise!" With Captain Thomas's order, some unnecessary equipment in the submarine was turned off to reduce the noise made by the submarine in the sea. However, the noises emitted by these can be said to be insignificant. The noises emitted by the submarine's engine and propeller propeller are the main sources of noise. Unless all power systems are turned off, the probability of the other party discovering them is still very high.

But they cannot turn off all power systems. If the enemy ships on the surface do not leave, their situation will be more dangerous.

On the sea, a German destroyer has approached this sea area, and the captain on the bridge issued an order. "Turn on active sonar! Pull this rat out!"

Sonar technology can be divided into two categories according to the working mode: passive sonar and active sonar. Simply put, active sonar only has ears, listening to various sounds underwater, and can only estimate the approximate direction of the target. Active sonar has an extra mouth, shouting with the mouth and receiving the echo with the ears to determine the distance of the target. These two methods have their own advantages and disadvantages. Active sonar can measure the point accurately, but it is easy to be exposed (when a surface ship turns on the active sonar, it is equivalent to shouting to the submarine in the water: "Hey! Brother, I'm here, my position is here, do you hear me clearly?". Vice versa); passive sonar can measure the point accurately, but it is inaccurate. The collision of nuclear submarines in later generations shows that passive sonar technology still has problems.

For the low noise emitted by submarines at rest, passive sonar cannot distinguish between submarines and noise in the sea. Active sonar can, because active sonar relies on specific echoes for positioning. Generally speaking, as long as the submarine does not land (sink to the seabed), active sonar can effectively locate the submarine.

The German destroyer turned on the active sonar and began to emit medium-frequency sound waves to the surrounding waters.

Ultrasonic waves are divided into three bands: low frequency, medium frequency and high frequency. Among them, the medium frequency has the best anti-interference ability. When using medium-frequency ultrasonic waves for active detection, it can effectively image submarines submerged in the sea. Ultrasonic waves in low-frequency and high-frequency bands are either far away but poor in accuracy, or high in accuracy but short in distance. They are not as suitable as medium-frequency waves, which have both good distance and good accuracy.

Unfortunately, this frequency band is also the physiological frequency band of most marine organisms (such as dolphins, whales and other large marine animals rely on medium-frequency sound wave echolocation for navigation and predation activities, etc.). Although some countries were equipped with medium-frequency active sonar in the late World War II and after the war, it was later discovered that the use of this sonar caused a large number of marine organisms that relied on echolocation to cruise blind, internal bleeding, and even death. Some dolphins or whales swam to unfamiliar waters and ran aground, or even washed up on the beach (which is what people think of as collective suicide). Therefore, the relevant animal protection organizations of the United Nations have formulated relevant measures to protect the safety of these marine organisms. Therefore, under the pressure of global public opinion, the military of various countries have abandoned the use of medium-frequency sonars on ships, and some countries have even gradually cancelled high-frequency sonars.

Unfortunately, it is a life-and-death war now, and no one cares about the safety of those marine animals.

Ping! Ping! Ping!

The dense sound waves hit the hull of the US submarine, and the sonar operator took off his headphones with a scream.

The cavity effect amplified the sound, and the sailors in the submarine heard this terrible sound clearly.

"Continue to dive to a depth of 50 meters!" Captain Thomas didn't know what the Germans were doing, but it was obviously not friendly, so he decided to do something.

Soon, the submarine dived to a depth of 50 meters, but the terrible ping! ping! sound became more dense.

Because the sonar operator took off his headphones, he couldn't hear that the German destroyer on the surface had dropped several depth charges.

Boom! The sudden explosion made all the sailors in the submarine stagger.

The first depth charge exploded more than ten meters to the left of the submarine, causing no substantial damage to the submarine, but another depth charge exploded two meters above the stern of the submarine. The huge shock wave blew a big hole in the front of the submarine, and the seawater rushed down.

"Drain the seawater from the bow! Urgently surface!" Upon hearing the damage to the stern, Captain Thomas immediately issued an order to surface. This level of damage is fatal to a submarine. If they continue to hold on, they can only go to see God; and he doesn't want to see God so early.

The submarine sailors are well-trained, and the captain's order was immediately executed. With the operation of the sailors, compressed air rushed into the ballast water tank at the bow, draining the seawater from the bow. The bow suddenly reduced its weight, while the tail was filled with seawater. As a result, the bow of the submarine was naturally lifted up, and the entire submarine quickly surfaced!

At this time, the third depth charge exploded almost against the hull of the submarine. Coincidentally, if it were an ordinary depth charge, it would only explode at the set depth. But the German depth charge had a proximity fuse, so the sinking depth charge exploded violently the moment it brushed past the rising submarine. The severely damaged submarine was broken into two pieces by the terrible impact and slowly sank to the deeper seabed.