Although he was confident that he would be able to force Germany to declare war on the United States, Roosevelt soon regretted it, not because he did it too late, because it was precisely in these two or three days that a major breakthrough was made in Germany's diplomatic work. The first was that Sweden in Northern Europe almost declared its accession to the Axis camp, which gave Germany almost complete control over all of Northern Europe.

You must know that although there is still a Finland that remains neutral, Germany is almost the only hope for the Finns to regain lost territory from the Soviet Union, and in addition to the fact that the Soviet-Finnish war is too badly lost, it is only a matter of time before the Finnish government falls into the arms of Germany. In fact, Finland was sandwiched between the Shili range of the Soviet Union and Germany, and its ties with the West were cut off, and it was inevitable to take sides between the Soviet Union and Germany. And the Finns could never defect to the Soviet Union, so it was almost certain that they would fall to Germany, and if it weren't for the fact that the mustache did not want to break with the Soviet Union now, he was afraid that Finland would enter the axis earlier than Sweden

Just as Roosevelt was about to immediately announce the full convoy to counteract the adverse effects of Sweden's entry into the Axis, an even more shocking news came that the Irish government, which had been neutral until now, announced that it had joined the Axis camp and immediately launched an attack on Northern Ireland, which had been occupied by the British

When the U.S. Secretary of Defense publicly announced that the U.S. Navy would henceforth provide full escort for the trade convoy between the United States and Britain, the Germans reacted much faster than Roosevelt had expected, and the next day the U.S. convoy sailing in the North Atlantic was attacked by German submarines, and a few days later there were fires everywhere, and even a convoy of German submarines sailed to the eastern coast of the United States.

And peace in the United States has been going on for a long time. No one expected to be attacked in the waters near the mainland, and there was no experience in anti-submarine warfare, and the merchant fleet had no restrictions on the use of wireless telegraphy, and they often reported their own positions, which gave German submarines important clues throughout shipping. The captains of the German submarines could not help but look at themselves as if they were hungry wolves rushing into a flock of sheep

The five submarines achieved breathtaking results in the first operation against the United States to break diplomatic relations, of which the U-123 submarine alone sank 10 merchant ships with a total tonnage of 91,720 tons. According to U.S. government statistics, in the first week from the initial attack, 32 merchant ships were sunk by submarines in U.S. waters. 257375 gross tonnage. This was much more beautiful than the beginning of the historical German submarine operation off the eastern coast of the United States, and the efficiency was almost doubled, while none of the five submarines were lost. The reason why there is such a big difference is mainly that the improvement of the quality of the torpedo fuse has made the regret that the German submarines in history repeatedly failed to explode the torpedoes has been avoided as much as possible (in other words, the German submarines suffered too much in history. If it weren't for the quality of the torpedo fuse. Churchill was killed before the Germans turned to Western Europe. Although even this is difficult to change the outcome of the final defeat of Germany)

What hit Roosevelt even more was the news of the attack on the fleet escorting four battleships to England, in order to guard against German submarines and aircraft. This time, the US Navy dispatched a huge fleet of 2 aircraft carriers, 3 battleships, 2 heavy cruisers, 4 light cruisers, and 20 destroyers to escort the convoy.

The root of the problem was still in the British, because they had only suffered a secret loss once, and the British government did not realize that the mechanism of their code compilation had been mastered by the Germans, so in their daily communications, they obediently told the Germans all the routes and departure dates selected by the escort formation, and the mustache immediately decided to use eight drop-shaped submarines that had just entered service to carry out this important ambush mission.

In this ambush battle, the advantage of the oxygen torpedo was fully reflected, because of the ultra-long range, even if it was set at a maximum speed of 50 knots, it could be launched at a distance of 10 kilometers, although the accuracy was not good at long distance, but this US-British combined fleet was too large, and the aiming direction was directly hit, and there was a great chance of hitting the enemy ship if it was lucky, so the accuracy was not a big problem.

For the light warships of the U.S. Navy arranged in the perimeter to protect the capital ships and transport ships, the huge power of oxygen torpedoes has also greatly weakened their role, if it is an ordinary torpedo, although it will basically sink after hitting these warships, but generally speaking, it can always jump on the water for a while, especially the light cruiser with a larger displacement (most of the new light cruisers of the US Navy have a displacement of more than 10,000 tons, which is actually equivalent to a heavy cruise. This is especially true because it can continue to block some torpedoes for the capital ships, and the oxygen torpedoes are too powerful (Note 1) to hit these warships and sink them directly, and they stay on the surface for a short time, so the first salvo can directly attack the capital ships and British ships in the circle after opening a gap in the perimeter

As a result, the US Navy had 2 light cruisers and 6 destroyers, and 2 of the 4 British battleships escorted by it were also sunk, mainly because these battleships were not yet in wartime configuration, the ship's personnel were insufficient, and the damage management after the attack was not timely enough, and the power of the oxygen torpedoes was too great, so the two battleships were all sunk. In addition, an American battleship was heavily damaged and had to be overhauled for at least three months

What makes the U.S. Navy even more embarrassed is that after suffering such huge losses, they have never been able to find those murderers. However, it is no wonder that the German submarine launched the torpedo from a distance of 10 kilometers, and although the oxygen torpedo was fast, by the time it hit the American warship (at least four or five minutes had passed), the German drop-shaped submarine had already completed its dive and began to move away. And the underwater speed of the teardrop-shaped submarines is much faster than the old ones, and the Americans only know the direction of the enemy, and it is not easy to find those submarines in this vast sea

Note 1: It is worth mentioning that the German Navy considered that the teardrop-shaped submarine generally must launch an attack in a submersible state, and the horizon of the periscope was limited, and the enemy ship could only be seen at a distance of 10 kilometers, so the original long range of the oxygen torpedo was wasted, so the German Navy made certain changes to its design, reducing the amount of fuel and liquid oxygen carried, so that its maximum range at a speed of 50 knots was reduced to 10 kilometers. Correspondingly, the charge of the oxygen torpedo has increased significantly, and its power is greater than that of Chinese origin. In fact, the Chinese Navy also discovered this problem, but because there was no urgent need for the war, it was not improved more than a year later than Germany, but the devil did not make such improvements until the end ......of the war because he had not given up the old idea of "destroyers launching torpedoes", which was almost impossible to succeed