As it became known after the war, the army ciphers of the Wehrmacht, simpler than the naval ones, were the first to split the Polish cryptanalysts headed by M. Rejewski. By 1939, they had even created Antienigma, a machine that could partially automate the decryption of intercepted German radio messages. In June 1939, the Poles handed over two such machines to the heads of the cryptanalytic services of England and France: after the defeat of Poland, Rejewski's group was transferred to Paris, and then to London, where the arrogant and proud British removed it from further work. However, even having received the machines and all the developments from the former allies, British intelligence was not able to immediately begin to decipher the naval codes, more complex and reliable than the army and aviation codes. To initiate such a decryption, it was required to intercept a sea-type "Enigma" with all the instructions.
This was done, and even then only partially, on February 23, 1941, when the Nazi armed trawler "Krebs" was captured near the Lofoten Islands. When inspecting the ship, the boarding party made sure that the cipher machine and ciphers were thrown overboard, so that only scattered rotors fell into the hands of the British. But this find prompted the Admiralty to organize a hunt for the "Enigma" of a marine model.
After a series of unsuccessful attempts, this hunt was crowned with success. On May 8, 1941, the escort of the convoy OV-318 managed to capture the fascist submarine U-110, on board of which the Enigma was found with all secret documents.
Here's how it was … At dawn on May 9, 1941, two boats U-110 and U-201, part of the "wolf pack", found the warrant of the ships of the convoy OV-318. The attack was carried out by U-110 under the command of Lieutenant Commander Fritz-Julius Lemp. As a result of the torpedo attack, he managed to launch two transports with a total displacement of more than 7, 5 thousand tons to the bottom. However, at the same time, the submarine betrayed itself. The English corvette Obreria quickly found it with sonars. Together with the destroyers Broadway and Bulldog, the corvette dropped several series of depth charges. As a result of the damage received, the submarine lost its stability and sank to a depth of ninety meters. To prevent the boat from being crushed, Fritz-Julius Lemp gave the command for an emergency ascent. As soon as the waves left the ship's wheelhouse, the lieutenant-captain jumped out onto the navigating bridge. What he saw did not bode well for the divers. Destroyers flew straight to the submarine, stepping up their speed. Their intentions to ram the boat were not in doubt. Lemp hastily gave the command to open the Kingstones and leave the boat. However, as it turned out, the chief mechanic of Eichelborn could no longer fulfill the command to sink the boat. Submariners hurriedly jumped overboard. The last, as befits the commander, the boat left Lemp, not even suggesting that his first order remained unfulfilled. Seeing that the crew of the submarine abandoned the ship, the captain of the destroyer Bulldog Baker-Cresswell changed his original intentions and gave the command to board the boat. The British formed a boarding team of ten experienced sailors under the command of Lieutenant Balmy. Seeing the British in boats approaching the submarine, Lieutenant Commander and First Officer of the Watch, Dietrich Leve, hastily turned towards U-110. However, Lemp did not manage to reach it. Some eyewitnesses claimed that their captain had been shot by English sailors, but Leve was convinced that Fritz Julius had simply let himself drown. As you can see, keeping the secret of the "Enigma" was a matter of honor for the German officers of the Kriegsmarine.
Photo taken by a British officer during the capture of U-110
After making sure that the submarine was afloat, the commander of the boarding team requested mechanics from the destroyer to board the U-110. By the time the mechanics arrived, Lt. Balmi had already discovered a naval version of the Enigma. Together with the cipher machine, the British got the ciphers that were in effect from April to June 1941. Inspection of the ship by mechanics showed that it was impossible to stop the sinking of the ship caused by damage to the stern ballast tank. Initially, the convoy escort command wanted to tow the boat to the shores of Iceland. But then, sensibly judging that this could indicate to the Nazi intelligence on the capture of the secret car by the British, it was decided to flood the boat. For the same purpose (keeping the fact of the capture of the boat secret), the British ships carefully surveyed the water area and fished out the entire team of the German submarine from the sea.
The received "Enegma" and the materials of the codes allowed the British to immediately start reading the radiograms encrypted with the Hydra cipher, and read them until the end of June. After that, British intelligence temporarily "blinded" in connection with the entry into force of the new tables, but a start had already been made: the government school of encryption and decryption, although with some interruptions the entire war could read the Hydra cipher. Moreover, solving this code helped the school, often called Bletchley Park (after the name of the country estate where it was located), successfully split a number of other codes: Neptune, Zuid, Medusa, Triton. In 1942, the Germans added a fourth rotor to the Enigma scheme, and the hunt had to start over. But the beginning had already been made, and decoding of the changed code was only a matter of time.
Of course, the process of splitting ciphers as a whole cost a lot of work, effort and expense: the school had about 10,000 people on its staff, and its equipment included several dozen computers, the prototypes of modern large computers. At the same time, computers were created specifically for this purpose by the famous mathematician E. Turing. But these costs were more than paid off by the results achieved.
Turing Computing Machine
To analyze all the information decoded in Bletchley Park, the Operational Intelligence Center (ORC) was created in the British intelligence system, headed by N. Denning, later Vice Admiral. One of the former employees of the center, P. Beasley, recalled: “We have established the exact number of submarines operating in the pack. We knew not only the content of the radiograms they sent, but, more importantly, we knew the content of the orders from the headquarters in Lorient, with which Dennitz systematically pumped up the commanders of the submarines. We knew the methods of operation of submarines, their average speed with which they could follow to patrol areas and back, we knew the length of their stay at sea, the characteristics of many commanders, their favorite patrol areas, as well as the exact meaning of short radio signals to transmit information about the detected purpose, location and weather conditions. We could follow the first combat campaign of each submarine in any area when following to the North Sea … We always knew when this or that submarine left for the raid and when it returned, if it did not linger at sea … We had accurate information about the power of everything the submarine fleet of the Germans and the location of each submarine … we knew which boats and how long were in the ports and when they had to go on the next cruise."
In developing the tactics of submarine warfare, Dennitz carefully weighed the pros and cons of the widespread use of radio broadcasts. The main thing he feared was radio direction finding, which allowed the enemy to establish the location of the submarine. But he did not allow thoughts, the radiograms are not only recorded, but also deciphered by the enemy, and therefore often trusted the radio waves with such information that helped the allies to destroy the boats.
So, in the spring of 1943, intercepting Dennitz's order, transmitted by radio, the British learned that the submarines attacked from the air should not seek to go to the depths, but to meet the bombers with long-range anti-aircraft guns. In accordance with this, the pilots of anti-submarine aircraft were ordered to immediately call for support and attack from different directions.
Having received the eagerly awaited detailed reports from submarine commanders about the first combat use of new acoustic torpedoes, the command of the fascist submarine fleet did not assume that the British also received this information and immediately used it to develop the Foxer anti-torpedo device. Of particular difficulty for the British were those German boats that acted alone, at their own discretion, and did not conduct extensive radio communications. But when such a boat returned to base, Dennitz sent escort ships to meet her. And paradoxically, these ships, which were supposed to protect the boat, pointed the enemy at it with their radiograms.
Finally, and this was the most important thing, from May 1942, the Allies began to successfully withdraw convoys from the patrol line of Nazi boats, thereby initiating a sharp decrease in losses.
Naturally, the British diligently concealed their acquaintance with the cipher correspondence of the Germans. They intensively spread rumors about the extreme ramification of their agent network, about the extraordinary achievements of aerial photographic reconnaissance, and especially about the miraculous capabilities of radar technology.
And it looks like disinformation has succeeded. When, twenty years after the war, Dennits was asked whether he felt that he had once been opposed by an enemy, as if reading his thoughts, the aged Grand Admiral replied: "No, I did not notice anything like that."
References:
Bush H. Submarine fleet of the Third Reich. German submarines in a war that was almost won. 1939-1945
Dennitz K. Ten years and twenty days.
Ivanov S. U-boot. War under water // War at sea. No. 7.
Smirnov G. History of technology // Inventor-rationalizer. 1990. No. 3.
Blair K. Hitler's Submarine War (1939-1942). "Hunters".
Biryuk V. Secret operations of the twentieth century.
