บท 308: Chapter 385 Operation Starvation (9)
Submarines, as the core of underwater power, often engage in maneuvers and confrontations with formidable enemies beneath seemingly calm sea surfaces.
However, this also leads to a very obvious problem.
You see, seawater acts as a massive conductor with excellent electromagnetic shielding effects. As a result, when submerged, submarines can hardly receive any television signals, mobile phone signals, wireless network signals, or most military radio communications.
So how do submarines maintain communication with their command? Surface and receive telegrams?
During the later stages of World War II, this was a dead end. As soon as a submarine surfaced, there was a high probability of it being targeted by anti-submarine aircraft.
Therefore, the communication issue for submarines became a global challenge.
At the inception of submarines as independent combat forces, some naval forces from various countries used surface warships that escorted submarines as relay information stations. Information was transmitted to the surface warships via radio, and then the warships would send out acoustic signals to the underwater using methods like tapping, which the submarines received through their sonar systems. However, this approach suffered from high distortion rates and virtually no secrecy, leading to its gradual abandonment after World War I.
Another method involved using radio buoys to send and receive messages. When using radio buoys, submarines needed to remain relatively stationary in the ocean. The buoys, connected to the onboard communication equipment via wires, would be deployed to the sea surface to transmit radio signals.
While this system addressed the submarine's external communication problem, it still faced significant limitations. Submarines had to maintain suspension underwater, making them more vulnerable to detection and attacks, thus compromising their survivability. Additionally, radio buoys were fragile and could be damaged in harsh environmental conditions.
Towards the end of World War II, communication experts discovered a way to enable submarines to receive communication even while submerged: longwave radio.
Seawater has a strong absorption effect on electromagnetic wave energy, but it varies for different wavelengths. The shorter the wavelength and the higher the frequency, the more pronounced the attenuation in seawater. However, longer electromagnetic waves can penetrate seawater to some extent. Longer wavelengths correspond to greater penetration power. Signals transmitted by very low-frequency (VLF) and ultra-low-frequency (ULF) radio stations can reach depths of several tens of meters to over a hundred meters underwater.
The term "longwave" is a general category. In practice:
- Electromagnetic waves with wavelengths between 1000 and 10,000 meters are called longwaves.
- Those with wavelengths between 100,000 and 1,000,000 meters are termed VLF.
- Ultra-longwave (ULF) refers to wavelengths between 1,000,000 meters and 10,000,000 meters (10,000 kilometers).
VLF radio stations can penetrate more than 20 meters of seawater. Towards the end of World War II, the German Navy began developing VLF communication systems. Submarines could receive VLF telegrams without needing to surface, operating at periscope depth. However, even at this depth, submarines remained vulnerable.
ULF radio stations can penetrate seawater up to 100 meters deep, which aligns with the typical operational cruising depth for submarines.
Therefore, when people refer to "longwave stations," they primarily mean VLF and ULF radio stations.
However, constructing longwave stations is no small feat. How large are the antennas for these stations?
Well, they are enormous—much larger than a mere 100-meter-high iron tower, which would only represent a small part of the longwave antenna!
Due to their extreme length, longwave antennas are not vertical; they lie horizontally. The purpose of a 100-meter-high iron tower is to isolate the antenna from the ground as much as possible, minimizing interference from ground waves during longwave transmissions.
In 1986, the United States built a longwave radio station consisting of two parts—one in Wisconsin and the other in Michigan. These locations were 258 kilometers apart and could work together or independently. The total length of their antennas was 135 kilometers, with eight transmitters—half operational and half backup—yielding a total power of 5.28 megawatts.
Driving along 135 kilometers would take over an hour.
Why such length? Because longwave transmissions have very long wavelengths, and antenna length generally relates to signal quality. For a 1000-kilometer wavelength ULF radio station, an 1/8 wavelength antenna (125 kilometers) is commonly used. While a 1/16 wavelength antenna could work, the signal quality would be lower.
After much consideration, Wilhelm finally agreed to construct a longwave radio station.
At this moment, the German submarines cruising in the North Atlantic received a telegram from the Wolfpack headquarters.
"Captain! A new target has been spotted," the message read.
The captain took the telegram, glanced at it, and his eyes lit up. "Nearly two hundred transport ships? Quite a catch." He compared the distance on the navigation chart, then leaned over the periscope to observe the surroundings. "Surface! Full speed ahead!" They were a bit far from the ambush point, and underwater travel wouldn't get them there in time.
As the submarine swayed, it slowly emerged from the water, riding the undulating waves on the sea surface.
"Stay alert, everyone!"
A sailor stepped forward, twisting open the hatch to the conning tower. Residual seawater, carried by sharp sea winds, poured down, causing an involuntary shiver among those nearby. Inside the submarine, the constant operation of machinery and engines maintained temperatures above thirty degrees Celsius year-round, akin to the scorching Sahara desert.
The crew donned heavy coats and climbed out onto the deck via ladders, smoking cigarettes while observing the sea conditions.
Yet, icy sea winds relentlessly swept into the submarine, dispelling the unpleasant odors within.
During World War II, submarines lacked the advanced air filtration systems of later years, resulting in rather unpleasant smells inside. The fumes from diesel engines, the odor of decomposing food, the stench from the toilets, and the crew's sweat—all combined to create an environment that made it easy to understand why "Gulong" perfume was so popular among German U-boats.
"Freezing!" Two bare-armed sailors in the engine room shivered suddenly, hastily grabbing clothes to put on.
The unwavering beliefs and determination of German Navy submariners formed the foundation for their high levels of discipline and mutual trust. In such circumstances, strict military discipline often took a back seat. Some German captains, known for their strict adherence to rules, allowed a more lenient approach to discipline onboard.
Originally, the German Navy submariners wore traditional navy blue uniforms for combat. However, wearing these in the confined space of a submarine was uncomfortable. Most German captains believed that as long as crew members effectively carried out their mission and performed admirably, they could choose their own attire.
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