Since 1941, the 10th Intelligence Directorate of the British Navy, which was directly responsible for protecting the communications of British ships, made several changes to the ciphers of the Navy, which, however, only slightly complicated the tasks of the Nazi cryptanalysts. So, already in the spring of 41, the Germans managed to decipher the code number 3 of the British naval forces, which made it possible to keep the German submariners aware of the movements of the British fleet in the Atlantic. Received "packs of wolves" and deciphered radio communications between the convoys and the main command of the British fleet regarding dangerous areas that should be avoided. German submarines attacked the Allied convoys in accordance with the instructions of the British command. On average, the fascist fleet received about 2,000 decrypted British radiograms, which informed about the composition of convoys, weather conditions in the area of hostilities, as well as the number of escort escorts.
October 1941 was marked by the active involvement of the United States in escorting convoys across the Atlantic, due to which radio traffic increased significantly. The Germans learned to distinguish on the air the signals emanating from the escort groups, as the most tasty targets for torpedoing by submarines. The British used characteristic call signs in negotiations, which were conducted exclusively between escort ships. "Convoy cipher" - this is how the German sailors called the specific code used by the British in such radio exchanges. German cryptanalysts worked so professionally that by October 1942 Karl Doenitz, commander of the submarine fleet of the Third Reich, received radio interception reports ten to twelve hours before the English fleet performed certain maneuvers. The Germans also successfully read the correspondence between the headquarters of convoy operations in Halifax and the British Isles. In particular, it contained information with instructions to the commanders of ships about bypassing dangerous zones off the coast of Great Britain, which, of course, was actively used by the "Doenitz wolf packs".
Eloquent WWII British posters of wartime talkativeness
The Krisgmarine surveillance service was able to "hack" and the old code of the merchant ships of England, as a result of which the submarines sank many civilian cargo ships, not particularly bothering to search. It is noteworthy that in England in the pre-war time, new codes for the merchant fleet were not introduced due to cost savings, and during the war all attention was focused on the Navy.
As a result, the British and the allies suffered heavy losses due to insufficient attention to the encryption of their own radio communications - several hundred ships with cargo went to the bottom along with 30 thousand sailors. In the North Atlantic until 1943, the Germans sank ships with a total displacement of about 11, 5 million tons, and this is without taking into account the considerable losses during the Norwegian campaign of 1940.
Eloquent WWII British posters reminiscent of the dangers of wartime talkativeness
How did the Germans manage the information received from the Kriegsmarine observation service? This can be seen in detail on the example of the defeat of the SC.122 and HX.229 convoys in March 1943. At that time, the Germans were able to intercept and decrypt 16 radiograms with detailed data on the routes of the convoys. Historical sources even indicate the exact dates and times when the Germans received the key information for the attack - March 4 at 10.10 pm and March 13 at 19.32 pm. The first radiogram described the details of the route of the convoy HX.229, and in the second the Admiralty ordered both convoys to evade the German submarine accumulation. It is noteworthy that this information reached the British command through intelligence - it is possible that after the decryption of the messages of the notorious "Enigma". As a result, the Germans threw 40 submarines on two convoys at once and sank 21 ships with a total displacement of 140 thousand tons, losing only one submarine. After the British described such a fiasco as "a serious disaster for the cause of the Allies."
Positive changes in the British Navy came only in mid-1943, when radio operators finally got a replacement for the tragically famous code number 3. The new cipher became much more resistant to breaking, and this proved to be a problem for Nazi cryptanalysts. But the merchant fleet, which the Germans drowned as if in a dash, received updated codes only by the end of 1943.
March 1943 was in many ways the apotheosis of the power of German cryptanalysis in the war with England and the United States. Their successes allowed the submariners to almost completely interrupt the sea traffic between the two countries, and only desperate heroes were able to lead their ships through the traps of the Kriegsmarine. The headquarters of the Navy in England said about this story: "The Germans were never as close to a complete disruption of communications between the Old and New Worlds, as they did in the first ten days of March 1943." The work of cryptographers from the British Bletchley Park did not give the Germans a final cut of the rescue aid from overseas. Typical crypto warfare at its finest.
Atlantic convoys were the first victims of intercepted radio messages from the British Admiralty
The Germans had one problem that they could not cope with until the end of the war: the lack of a full-fledged staff of translators capable of quickly translating arrays of decoded interceptions from English. Receiving up to 2,000 radiograms of British convoys, the Kriegsmarine surveillance service simply did not have time to translate the entire wave of information, not to mention a full-fledged analysis. But what was transferred was quite enough for the timely guidance of groups of submarines to the Atlantic convoys.
In an original way, German cryptanalysts managed to break the naval gamma cipher, the key to which was a special code book. The hacking was possible after a careful analysis of the message addresses, which were always at the beginning of the cryptograms and, which was an English mistake, were encrypted with the same code. There were a lot of cipher programs, which made it possible to recover, bit by bit, individual fragments of the book, and later the whole of it.
Karl Dönitz is the "hero" of the Time cover
“I have already mentioned several times about the wonderful work of the German decryption service, which has repeatedly managed to uncover the enemy's codes,” wrote Grand Admiral Karl Dönitz in his memoirs. As a result, the command of the submarine forces read not only English radiograms and instructions to convoys about the route of movement, but also the Admiralty's report on the dispositions of German submarines (in January and February 1943), which was broadcast daily by radio and in which the known British intelligence and the proposed places were indicated. finding German boats in various areas. " Doenitz also points out that the deciphering made it possible to compose a picture of the level of awareness of the British about the disposition of German submarines, as well as their ability to determine the waters of the action of "wolf packs". In this regard, the thought comes: weren't the British so wrong with their absurdly secret "Ultra" program, the victims of which, in particular, were the inhabitants of Coventry?
