Flashback: Mi5 in World War Two
In the Pacific Theatre during the Second World War, Japanese forces were relentless in their attacks and victories over the Allied forces in South East Asia and in the Western Pacific. The string of victories from December 7th 1941 to May 20th 1942 included – the attack on Pearl Harbor, the capture of Thailand, Malaya, Wake Island, Guam Island, the Philippines, Hong Kong, Singapore, Burma, Dutch Indonesia and the invasion New Guinea. Japanese naval and air assets roamed the Pacific attacking Allied bases in Australia, Ceylon, east Africa, and even the west coast of North America at will. But, the sea battles of Coral Sea and more specifically at Midway, in May / June 1942 put a halt to the wave of Japanese victories.
What happened at Coral Sea and Midway? Why did American Navy stop the Japanese advance at these critical points – Were American aircraft and ships better than Japanese equipment? – No, production of new classes of ships and aircraft would not arrive in the Pacific until 1943. Did American forces have more men, aircraft and ships? Again no, the tide of the American industrial strength would not be felt in the Pacific until 1943. Was it better leadership? Admiral Chester W. Nimitz, who would superbly command U.S naval forces in the central Pacific from the early days of 1942 until the end of the war, was equally matched by Admiral Isoroku Yamamoto overall commander of Japanese forces during the battles of Coral Sea and Midway.
The difference was Allied (American, Australian, British, and Dutch) intelligence and cryptanalyst who co-operated in the breaking of the Japanese naval code JN-25. JN-25 a military forces code system (the 25th Japanese Naval system identified) was the most used and secured communication system used by Japanese naval forces at the beginning of World War Two. Introduced in 1939, JN-25 code replaced the earlier code “BLUE” (as named for the blue binding that the intercepted code messages were placed in); JN-25 an enciphered code, producing five numeral groups in the traffic which was actually broadcast, was frequently revised, with new code books being created on a regular basis.
Before December 7th, 1941 interception of JN-25 transmissions was limited, thus Allied cryptanalysts had little material or opportunity to decode this new code. But, from December 1941 to May 1942 the increased radio traffic between Japanese units allowed U.S. Navy’s signal intelligence cryptanalysts in OP-20-G to crack the current version of JN-25 just in time for Coral Sea and Midway.
Commander Joseph J. Rochefort (1900-1976) commander of Station Hypo (Hawaii) with assistance from the teams at Station Cast (Cavite, Philippines) and the British Far East Combined Bureau these elements of Allied cryptanalyst were able to crack the JN-25 code. Rochefort’s team in Hawaii was also able to convince Admiral Nimitz that the next major attack in the central Pacific would be the Midway Island chain. This was done by having an unencrypted emergency (false) message sent to from Midway – that AF’s need for assistance in the repair of its water desalination system (with AF being – Midway’s codename) to Pearl Harbour. The Japanese listening posts intercepted the message and reported the fact in encrypted messages to naval command. Rochefort’s team intercepted these messages, and with the ability to read the JN-25 code confirmed that Midway was the next target of the Imperial Japanese Navy. An addition benefit to this trickery was that in follow up messages the Allied cryptanalyst were able to intercept and decode the timing of the attack – early June 1942.
The advantage of superior cryptanalysts, code breakers, scientists, technology, and knowledge in the field of intelligence provided the information which enabled the Allies to defeat the Japanese at these two critical battles. Nimitz positioned his outnumbered forces strategically where he could ambush and defeat the Imperial Japanese forces at Midway. The decimation of Japan’s aircraft carrier fleet and senior naval aviation personnel would be a serious problem for the Japanese throughout the remainder of the Pacific war. For the Allies the Battle of Midway was a deceive victory and the turning point in the Pacific, a victory that may have not happened without the Allied code breakers.
In relation to information and information warfare, JN25 and the cryptanalysts group involved within the U.S. Navy; this is a prime example of information manipulation, interception, cryptography and misdirection to achieve a strategic victory. Ultimately turning the tide in the Pacific.
In terms of cyber and information warfare, old is new, and our contemporary information age it is an ongoing continuance.
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