The Usage of Cryptography in the Battle of Midway

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Cryptography defines the process or study in which classified information is transformed into undecipherable text for protection. In World War II, cryptography was used immensely by multiple nations worldwide. Countries used this form of secrecy to protect valuable information from being revealed, when communicating.The use of codes, cipher and others, led to the downfall and success to several countries. Three ways cryptography was utilized was with JN-25, the enigma cipher and the Type B cipher machine.

JN-25 was a Japanese naval code. In comparison to German codes which used mechanical equipment, Japanese naval codes were “book ciphers”. Book ciphers work when the sender creates a message, and then uses a code book to encode it. First, groups and numbers are to replace common words and phrases. Then, character by character, the remaining text is encoded. After the message is transmitted, the receiver has to decode it with a corresponding code book by looking up the groups and numbers. The decryption of JN-25 led to the irreparable damage inflicted on Japanese fleets during the Battle of Midway. In early 1942, the U.S decoded messages revealing that the Japanese Navy was planning an imminent attack on a target coded as “AF”. American cryptographic intelligence units were not familiar with AF. Because of this, Station HYPO, the “United States Navy signals monitoring and cryptographic intelligence unit”, (in text) set up an experiment using an underwater cable connecting Pearl Harbour and Midway, which was susceptible to Japanese interception. Station HYPO ordered a radio station (by cable) in Midway to broadcast the uncoded message that Midway’s desalination plant was down. Later, the U.S intercepted a message using JN-25 that the desalination in AF was down. Thus, the target AF was confirmed as Midway. Station HYPO also succeeded in gaining the timing of the attack being late May to early June. Commander of the U.S pacific fleet Chester Nimitz, took the risk using the only three remaining carriers, to ambush the Japanese Navy at Midway. The attack was a massive victory for the U.S as they sank four Japanese carriers while only losing one of their own. Over 3000 Japanese soldiers and 250 aircrafts were also lost. The decryption of code JN-25 was the starting of the decline in Japan’s military successes. This battle being the first major victory for the Allies in the Pacific, it was also a huge turning point in the war.

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In addition to the JN-25 code, the Enigma machine was an enciphering machine used by the Germans to send encoded messages using the Enigma code. This code was invented at the end of WWI by a German engineer named Arthur Scherbius. Polish mathematicians managed to crack the enigma code and they later shared their found information with the British. Although during the upsurge of the war, the German armed forces added more security by daily changing the cipher system, making the decryption of this code extremely difficult. The machine was made with rotors that were interchangeable. These rotors could then be placed at different adjustments to receive different substitutions. The Enigma cipher and it’s decryption was probably the most important codebreaking achievement for the Allies. Alan Turing was a British mathematician who worked at Bletchley park where him and several others, would decipher military codes and ciphers used by Germany and their allies. His main focus was to crack the Enigma code. During the Battle of the Atlantic, Allied ships were facing heavy losses as German navy communication was too complex to decode.

Eventually, using previously gained information about the Enigma (gotten from a captured U-boat), and Turing’s newly developed technique “Banburismus”, the messages were able to be deciphered from 1941. This was pivotal in helping the Allies. With the newly revealed messages of attacks and U-boat routes, the Allies were able to safely move their convoys away from U-boat “wolf-packs”. Since Britain is an island, food and supplies are heavily imported from several countries including the U.S. With German boats sinking British supply ships, the Germans were on their way to starving Britain out and they were intercepting equipment and supplies needed by Britain to survive the war. This was a time where without the decryption of this code, Britain’s future would’ve been disastrous. Deciphering this code also meant that Germany was slowly losing control and being overpowered.

Along with JN-25, the Type B cipher machine was also used by the Japanese. The Type B cipher machine was an encryption machine codenamed “Purple”. This machine contained two typewriters, a switchboard and an electric rotor. Like the Enigma, Purple had a secret key that changed everyday; if the machine was stolen, it would be useless without the key for that day. The rotors would rearrange when a letter was inputted and mixed the alphabet for the next letter. The codes Purple produced was exceptionally hard to decipher as it would go through millions of cipher alphabets, before a previously used one would be repeated. It was used by the Japanese Foreign Office to send extremely important military secrets. With the trust of German officials and Hitler, a Japanese baron bought a commercial Enigma machine. The Enigma was bought so that Japan would be able to develop a new version. This newly developed machine was codenamed named “Red” by the U.S. The Japanese Navy used Red from 1931 to 1936 when the system was decrypted by Americans. Since the U.S did not keep the decryption of Red a secret, the Japanese found out, and were working on creating a new machine. This machine was what is now known as Purple. This system was fairly hard to use and so it would only be used to send top level military secrets. Although because of the inexperience, workers had with the system, messages would sometimes be sent in the Purple cipher and the previously cracked Red cipher. This helped the Americans decipher the messages. Eventually Purple’s encryption method was fully discovered, but the daily switching keys proved to be a massive obstacle. Lt. Francis A. Raven managed to find a pattern in the keys used, and the Americans fully cracked the Purple cipher. With the top level information obtained, the U.S learned of military communications and Japanese Naval troop movements. Information about the Pearl Harbour attack was also revealed, but the U.S did not use that information usefully, when they could’ve prepared and ultimately prevented the devastating damages inflicted.

As seen above, cryptography played a huge role in defeating other nations/countries. With valued military communications being intercepted, it led to the overall downfall of certain countries. As German communications were constantly being studied and intercepted (like at Bletchley Park), their advances and attacks were already revealed to the Allies leading to the defeat of Nazi Germany. Cryptography was a crucial role in defeating the Axis powers. For the Allies, breaking the Axis powers’ communications gave them a massive advantage; it saved many lives and shortened the war, by what some say as two years. The use of ciphers and codes are still massively used today, and they are only getting more advanced and better. Learning from the machines and the mistakes made in the past, they play a huge part in today’s technological society.

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