U-boats had remarkable success against Allied convoys by attacking on the surface at night (when they could not be spotted by Allied sonar, or ASDIC), destroying merchant ships with torpedoes and then plunging to dodge the counterattack by escorting warships. They caused massive losses in 1941, sinking 875 Allied ships. But the damage was done: by the end of 1942, Britain's ability to trade with its colonies and defend itself from invasion had been severely weakened. The United States came into the war in 1943 and brought a new dimension to the struggle when it began producing submarines of their own.
The most successful tactic for defeating U-boats was to hunt them down before they could strike again. Convoys provided a protected environment where U-boats would be forced to surface and refuel or run out of fuel and have to return to port. From there, they would be sent back out to patrol off the coast of Europe until another convoy was heading toward danger. Convinced they were doing God's work, German submariners went to sea eager to meet their fate with honor. But they were no match for the resources of their enemies: between June 1941 and May 1945, only 56 U-boats were lost while patrolling European waters. The other 1170 were either destroyed or captured by British and American forces.
In conclusion, the defeat of the U-boat campaign proved to be one of the great successes of World War II.
There are 783 U-boats. The battle resulted in a strategic victory for the Allies (the German blockade was broken), but at a high cost: 3,500 merchant ships and 175 warships were sunk in the Atlantic for the loss of 783 U-boats (the majority of which were Type VII submarines) and 47 German surface warships, including four battleships (Bismarck).
The sinking of the Bismarck on 27 May 1941 made her the first battleship to be lost by a country other than the United States or Britain. She was quickly replaced by another battleship, Prince of Wales, which meant that Germany had lost two battleships in less than a year. This is more than America or Britain had lost during all previous wars combined.
This is also more than the entire Japanese fleet at Midway Island at the beginning of the war. Although U-boat activity against Japan decreased after the Battle of Midway, this still represents a large percentage of Japan's available naval power.
Furthermore, the Bismarck's destruction ended Germany's hopes of winning the war before Russia entered it. Without this victory, Hitler might have been willing to risk everything on a final attempt to conquer Russia instead.
Finally, the Bismarck's demise proved that battleships were obsolete. They were too expensive to build and maintain and could not be used effectively without support from air power and submarines.
The U-boat was extremely stealthy. They would stay underwater until they located a target. By 1915, the North Sea had been proclaimed a war zone, and U-boats had adopted an unrestricted submarine warfare posture. Germany officially proclaimed that its submarines will attack any enemy commerce ships in the waters surrounding the United Kingdom. This would lead to Britain closing off certain areas of the ocean for safety reasons and refusing to trade with other countries who were friendly with Germany.
The U-boat changed naval warfare by making attacks on warships effective rather than just a matter of luck. Before the advent of the submarine, wars were won with ships. The more ships you had, the better chance you had of winning. But now that submarines could sneak up on ships undetected, the game changed. A ship might have the best crew in the world, but if it's not protected from these underwater assassins, then it's only a matter of time before it's gone. The U-boat made attacks on warships effective by removing their advantage over smaller boats: the ability to fight back. Once a U-boat got within range, it'd release torpedoes into the heart of a ship causing massive damage and very likely leading to its destruction.
Germany started the First World War with its navy impotent because most of its vessels were still bottled up in ports. But by the end of the conflict, it became one of the most powerful fleets in the world.
German U-boats targeted Allied ships in the Atlantic in order for Europe to cease getting supplies from the United States. The techniques utilized by the Allies to ultimately win the Battle of the Atlantic through strengthening naval tactics and aviation. As a result, the Allies were able to sink the German U-Boats. Therefore, the war continued into 1945.
During World War II, Germany waged an aggressive submarine warfare campaign against Allied shipping. This was done in an effort to cut off supply lines to Europe's enemies and force them to accept German terms for peace. The most successful country at sinking enemy ships was Germany itself. However, they could not keep up with the numbers of ships being built in America and Britain. Thus, they decided to use all available resources to fight a defensive battle until they could build more submarines. The Germans used two main methods for hunting down merchant vessels: wolfpack behavior and radar detection. Wolfpacks consisted of several U-boats operating together that would move in unison to find prey. This method was used because U-boats were limited in number and needed to be used efficiently. If one boat was sent on a mission that didn't work out, another could take its place.
The Germans also used radar detection to find ships. This technique is based on transmitting radio signals at various frequencies which can be picked up by receivers attached to ships' antennas. The higher frequency the signal, the farther it can travel before losing strength.
During WWI, the Germans lost 178 U-Boats, more than half of their total fleet, yet were unable to substantially affect British supply lines. The second reason was the development of sonar, a novel technology pioneered by the British during the interwar period. Sonar works by transmitting sound waves into the water and listening for any returning echoes from objects below the surface. Modern versions use computer technology to analyze the sounds that return to determine what is causing them and where they are coming from.
WWI also saw the introduction of many new technologies that have been used since then including: radar (1939), which is similar to sonar but uses radio waves instead; hydrophones (1930s-1950s), which are sensors that detect sound waves underwater; and magnetic field detectors (1960s), which work on the same principle as geiger counters but can measure the strength of the field rather than its presence or absence.
These technologies enabled naval commanders to locate submarines with great accuracy, giving them the opportunity to attack them first before they could strike at their targets. They also provided evidence of where submarines had been so that countermeasures could be taken if necessary.
Some scholars have suggested that nuclear power should be included here as well, but this requires further investigation.