Widger said:
I noticed that the Snows talked about the US breaking the Japanese codes, didn't they get assistance from Bletchley Park in this matter?
I have the book of the series which is a very worthwhile project but the one thing that irritates me is the way the breaking of the Japanese codes was just a throw away line in the book. I didnt see the programme but assume it was just as throwaway there.
Bletchley Park did have a role in that it was the first to break JN25 the superenciphered code the Imperial Navy used. The work was then taken over by the British station in Singapore which cooperated with their US equivalent in the Philippines. But by this stage of the war, May 1942, both the Singapore and the Philippines stations had gone and the US station at Hawaii had the lead on breaking JN25, assisted by the British who had retreated to Colombo.
It was a brute to get into. A massive codebook encoding phrases and key words into five-figure groups. Having encoded the message, the operator took a randomly chosen string of five-figure groups of the same length from what was itself a random five-figure cipher book. He wrote the cipher groups out under the encoded message and added each cipher group to each code group. So if a code group was 11123 and the cipher group underneath it was 22113 then the group the operator sent was 33236. So to break it you had to somehow strip off the cipher before you even got to the code, a very difficult task. Not as difficult as you might imagine but nevertheless very hit and miss with a lot of skill and luck needed together with the odd dash of brilliance.
Throughout May 1942, the US Navy chiefs in Washington refused to believe persistent intelligence reports from both Hawaii and Colombo that Midway was about to be invaded. It was Colombo which intercepted the key message that showed it was. But it was the Hawaii Commander Joe Rochefort and his codebreakers - working day and night fuelled up by amphetamines - who quite brilliantly managed to break Yamamoto's final operations order to his commanders. Rochefort said: "We could tell them what was going to happen, such things as where the Japanese aircraft carriers would be when they launched their planes, degrees and distance from Midway. Then of course the rest of the dispatch would be the strength of the attack and the composition of the attack forces and so on."
The only thing they couldnt get from the Yamamoto ops order was the precise timing, which was enciphered a further time. But they could get that elsewhere. The British role here was fairly minimal and I wouldnt have wanted to see it mentioned in relation to Midway in either the book or the programme. It was Rochefort's role which should have been recorded a bit better. The above information helped ensure the US won. It's the sort of intelligence any commander would give his eye teeth for and was absolutely crucial. Should have been mentioned. They didnt have to go into all the detail I have to give Rochefort the credit he deserved.
Some things never change however. Rochefort had produced a brilliant piece of intelligence but he had also proven his bosses in Washington wrong and in doing so had made them look foolish. Nimitz recommended him for the Distinguished Service Medal but the big chiefs back in Washington ensured he never got it and had him posted to San Francisco to manage the commisioning of a new dry dock, a total waste of his talent. He was posthumously awarded his DSM by Ronald Reagan in 1986.