On the sea more than 300 kilometers away from Campus, the mighty and majestic US fleet was slowly moving forward, and in the dark night, only the low roar of the ships could be heard, but there was not a trace of light to be seen. Pen, fun, and www.biquge.info

Nimitz and Hewitt were very cautious people, and the closer they got to the Rio defensive circle, the more cautious they became, and of course the lighting control was not overlooked. In order to maximize the safety of navigation, Nimitz also studied a number of plans, specific to the lines of action of the two fleets, and after many considerations and considerations, he designed different plans:

The two fleets as a whole moved southward parallel to the east coast of Brazil, with the transport fleet in the inner ring and the main fleet in the outer ring, separated by about 200 kilometers from each other, while the main fleet as a whole advanced more than 200 kilometers -- 250 kilometers southeast of the transport fleet.

This formation was of great use, and the current threat to the U.S. fleet consisted of three main components: first, the hidden German fleet; second, the Luftwaffe, with Rio as its main base; Thirdly, the German wolves hidden under the water. It is impossible to eliminate all three of these dangers, and there must be trade-offs. Nimitz was distinguished by the degree of danger, with the higher the ranking, the higher the degree of danger.

If you want to avoid the attack of shore-based aviation, the farther away from the coastline is better, but in this way, the possibility of running into the German fleet increases. If the German fleet ran into the transport fleet, Nimitz believed that the enemy would be able to send all the main forces of the transport fleet to the bottom of the sea in just one hour, so he could not go too far into the deep sea.

At the same time, Nimitz believed that the German submarines that could operate in the waters of Brazil should all be large submarines -- otherwise, it would be difficult to have a long range, and the closer to the coastline, the shallower the sea depth, the easier it would be to find the traces of enemy submarines, and it would be much easier to counter-submarine, so they should be as close to the coastline as possible, but not too close, otherwise they would become the target of shore-based aviation

It is not possible to mix the main fleet and the transport fleet, because the speed of the two sides is different, and the fleet is too large and can easily become the target of submarine attacks. It's not good to stay too far, it's not good for escort.

After combining various factors and weighing the pros and cons, Nimitz chose this formation - he believes that no plan or tactic is perfect, and the key is to keep the danger to a minimum.

His analysis is very reasonable, the XXI and XXIII class submarines currently used by the German army in Brazilian waters are both of the 2,000-ton class, and shallow sea activities are not suitable and cannot be carried out. But there is one thing that the Americans did not expect was that the goal of Krak's mobilization of more than 30 submarines was not to land the fleet, but to restrain the main fleet of the US army.

This was surprising to many, and even Hintz believed that submarines should be prioritized against the landing fleet, citing two important reasons:

First, compared with the main fleet, the US landing fleet must have a stronger anti-submarine awareness and anti-submarine awareness.

Second, it doesn't make much sense to attack the landing fleet, once the German South Atlantic detachment destroys the main fleet of Nimitz, it will be able to completely control the sea in the South Atlantic, so what is the landing fleet in front of aircraft carriers? It's just a pile of scrap copper and rotten iron!

These two reasons convinced everyone.

In order to pursue the maximum ambush effect, several submarines gave up the attack on the landing fleet two days ago, and only concentrated on concentrating on building an ambush circle in the south.

Every day, reconnaissance planes taking off from Rio had to relocate and sort out the positions of the US fleet -- the purpose was not to use aviation to attack, but to analyze the feasibility of Nimitz's southward path and arrange an ambush.

Now, this opportunity has finally arrived!

Nimitz was not ignorant of the impending risks, on the contrary, he, like all American admirals, attached great importance to anti-submarine.

In this time and space, German submarines posed a mortal threat to Britain and the United States, and in order to improve their anti-submarine capabilities, Britain and the United States made a series of strange moves and constantly strengthened their own response strategies.

The first step in the escalation of the confrontation between Britain and the United States was to improve the original isolated, separately launched depth charges into hedgehog shells. Although the charge of the hedgehog shell is not as good as that of a depth charge, it uses a system launch module, and a single launcher has 24 barrels and is tilted forward 45 degrees (so many barrels are close together to resemble a hedgehog stinger, hence the name). The Hedgehog Bomb Launcher is usually mounted on the bow deck. When fired in a salvo, 24 hedgehog shells were fired one after the other at very short intervals, forming an oval-shaped barrage in the sea, from which it was difficult for the submarine to escape once it was enveloped in a barrage.

In general, destroyers can be installed with one set, 10,000-ton treaty-type cruisers can be installed with two sets, and in antisubmarine warfare, there are usually two or four destroyers in a group, and at the same time, they also have the ability to quickly reload, and they can dump hundreds of hedgehog shells within an hour, until the submarine officers and men under the sea surface have a mental breakdown.

After 1942, Britain and the United States introduced large aircraft anti-submarine, when the weather is fine, submarines within 30 meters of the surface can be found, and the discovered submarines are usually destroyed by the hedgehog bombs dropped by aircraft, even if they cannot sink German submarines, they can force the opponent to dive deeper and deeper. In addition to traditional visual detection, large searchlights, radars and other auxiliary observation facilities are also installed on the aircraft, making it unsafe for the U-boat to float and charge at night.

In order to cope with this situation, the German army introduced innovative snorkel technology, which allows the submarine to be charged without having to float up and only exposing the snorkel, which greatly improves the survival rate of the U-boat. However, the good times did not last long, and the US countermeasure -- the use of microwave surface search radar -- came into being.

This radar is produced by the United States using the British magnetron, with a power of 50KW, a pulse width of 1.3~2usec., and a working frequency of 3000MHz, which the US military calls SG-1 radar. It can capture enemy planes flying low on the sea surface that are missed by low-frequency radars, and can also capture periscopes 9,000 meters away and large ships 30 kilometers away, and the snorkel smaller than the periscope can be found at a distance of about 5,000 meters. Since this distance exceeded the G7 torpedo launch range, it was very threatening for U-boats.

Experienced U.S. radar soldiers use the SG-1 radar to search the surrounding sea surface in circles at night, detect suspicious bright spots and track them, and then read the data directly from a mechanical calculator, most of the time these bright spots are real snorkels, and the U.S. military either uses hedgehog bombs to blow up and sink U boats, or force the adversary to give up the attack and dive underwater to achieve escort safety measures.

In response to the terrible radar detectives, the Germans used a variety of radar warning aircraft - some to capture the radar signals of surface ships, some to capture the radar signals of microwave radars, and some to capture the radar signals of aircraft (they usually have different wavelengths), but the British and the United States would also change the frequency in time to disable the warning receivers. For example, the SG-1 radar was improved and used a frequency of 10,000 MHz, which immediately abolished the warning system painstakingly developed by the German army.

In 1943, the German army began to improve the material of the snorkel at the prompting of Hoffmann, changing the upper end of the snorkel exposed to the surface of the water to a composite material that could weaken and absorb radar waves - this is a consideration that kills two birds with one stone, and these materials and coatings can also be used to improve the stealth performance of aircraft and vehicles in the future.

This measure is very effective, the special coating successfully developed by German scientists successfully compressed the detection range of the SG-1 radar to about 2500 meters (at night), coupled with the German army's use of long-range, high-speed oxygen torpedoes, before the US military found the snorkel signal is enough to occupy a favorable launch position for attack, which allowed the German army to take the lead in the confrontation in 1943, a large number of British and American freighters were sent to the bottom of the sea, coupled with the growth of the German surface fleet and the victory of the Azores base aviation confrontation, In the end, the best anti-submarine method to force the Allied transport fleet to adopt was to ignore the German submarines and simply use the direct rush method to make a hard break.

By the end of 1943, the confrontation had escalated again. The United States has focused on improving in two areas: first, the development of advanced active sonar; The second is to improve and increase the power of the microwave search radar.

The United States and Germany have taken different development paths due to different strategic considerations: the US military focuses on the development of active sonar, increasing the exploration distance of sonar from about 2,000 meters to more than 4,000 meters, and also using dual-drive joint exploration -- that is, two destroyers simultaneously detect a sea area and quickly exchange information for comparison. In addition, German scientists have also developed a rotating base array, which has changed the single beam scanning in the horizontal direction generated by a single sonar through mechanical rotation to multiple sonar for sector partition scanning, which greatly improves the exploration efficiency.

On this basis, Germany introduced the unprecedented XXI-class submarines, which were real "submarines", the whole submarine highlighted the underwater streamlined design, greatly reduced deck guns (later completely eliminated at Hoffmann's suggestion), and the streamlined body could achieve a faster speed underwater than a freighter (whether Victory or Liberty). On the other hand, the submarines of this class are equipped with a system that uses hydrogen peroxide as an oxidizer and has a primary primitive AIP function, and the incubation time has been greatly enhanced, from the previous few hours and more than ten hours to 54 hours, and by the time of the XXIII class submarines, the full incubation time has been increased to 88 hours due to the further expansion of the displacement.

At the same time, all other advanced technologies have been introduced into this class of submarines, such as double-layer hulls, which have another layer outside the pressure-resistant shell, and passive sonar and other facilities are set outside the pressure-resistant shells to improve space utilization; The use of rotating base array sonar that can detect precise azimuths and distances allows submarines to launch torpedo attacks without raising the periscope; Wire-guided torpedoes were also used.

Originally, the wire-guided torpedo developed by Germany in World War II was called "Skylark", which sounded very gentle, but after Hoffman instructed to use the wire-guided function on the basis of the G9 Super Oxygen Torpedo (Lance Modification), this thing became a murderous name - Tiger Shark!

The 29 XXI-class submarines carried torpedoes that were half tiger sharks and half spears, and the 2 XXIII-class submarines that led the show were all majestic tiger sharks.

They waited in the deep sea for their prey to come crashing into the door......

ps: There is a change in the night......