Well, the enigma codes recovered by two Officers of His Majesty's Royal Navy was quite important. I believe that at least one of the two died in the process...

...Then Hollywood came along and re-wrote the story.

[edit]typos, and history check, late October 1942, from U-559, and two sailors died in the process. It seems that several had been recovered before from German weatherships, which had lead to earlier code breakthroughs.

It also appears that some German personnel involve with Enigma failed to believe it had been broken, even when the documentation was released in the 1970s...

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After a substantial amount of badgering from the British press...

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Indeed & I don't know the answer either.

While on the subject of Enigma, the codebooks recovered from U110 by HMS Bulldog on 9th May, 1941 would qualify as documents. These were a vital breakthrough & equally as important as the machine itself. There was already an example of the Enigma machine at Bletchley Park, thanks to the efforts of Polish cipher experts supplying a set of rotors & drawings of the rest of the machine. This had enabled a working example to be built & the Luftwaffe codes were being deciphered during the BoB in 1940.

Another vital breakthrough was when HMS Petard recovered an intact example of the latest 4-rotor Enigma machine used by the German Navy together with the code books from U559. This was the incident on 30th October 1942 when two members of Petard's crew lost their lives. It was thanks to the efforts of young canteen assistant Tommy Brown, who it was later discovered had lied about his age to join the RN, that the vital codebooks were recovered intact. http://www.royalnavalmuseum.org/info_sheets_enigma.htm

PS. I think that Winston Churchill would have regarded these as possibly the most vital documents recovered during WWII. He described the 'U-Boat menace' as his worst nightmare, so serious that if allowed to continue could affect the outcome of the war.

It can be that and be entertaining at the same time.
Though I've never seen it, so I have no room to comment.

I'm going to guess the capture, early on, of the German plans to invade through Belgium.

If I recall, a light plane crash landed on the Belgian side of the lines and before they had a chance to burn the papers, the Belgians captured the officer's briefcase, containing the plans to invade throught the Ardennes.  It was shown to the French/Allied command, but since it didn't fit into the mindset of the Allied commanders, it was discarded as a "plant" and no preparations were made in the dispositions.

Had the Allied command paid heed to the plans, they could have moved troops and armour to head off the attack.  After all, the Allied had more, and better, tanks than the Germans.  The Germans had the better tactics for using tanks.

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That is indeed significant, and it may be argued that it is the most substantial document, but I would suggest since it was ignored, it was rendered ineffective.  The document I am referring to was indeed acted on and was quite significant.

If nobody gets the answer by later today, I'll reveal the document.

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Indeed. WWII covers a long period of time & several different theatres over a vast area in almost every part of the world. With no knowledge of the theatre involved or who considered this document vitally important it's extremely difficult even to hazard a guess.

Hagar,

the contents of the above post is a huge hint.

On March 31, 1944, two Japanese flying boats crashed into the sea off the Philippines, killing Yamamoto's successor, Admiral Koga.  A passenger who survived was Vice Admiral Fukudome.  Philippine guerrillas captured Fukudome.  Fukudome posessed a document titled Operation Z, or the Z Plan.  It was the Japanese plan for the defense of the Marianas Islands.

The Japanese made life very difficult and short for the Philippino people until Fukudome was returned back to them.  But the guerrillas realized the importance of that document, so it was smuggled out of the Philippines and was translated by Nisei.

The Japanese were concerned about the missing documents, so Koga's successor, Admiral Toyota made minor changes and renamed it as Operation A-Go.  One significant culmination of this battle plan, that the Allies learned about from the recovered documents led to what we know as The Great Marianas Turkey Shoot.

......and as Paul Harvey said, "and now you know the rest of the story"

I'm glad he said "arguably" as this sort of question is incredibly subjective.
As has already been suggested the enigma codes would be "arguably" more important as the finding of them had a bigger influence on WW2, as a whole, rather than just one battle. Didn't the Japanese use a form of the enigma machine? and wern't their messages being decoded too?

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Indeed & there was a Japanese section at Bletchley Park where much of this work was done. At its peak there were 10,000 people working at Station X, as it was known, from all parts of the world & all walks of life. Many of the decipherers in the Japanese section were Americans. I discovered this & many other facts about the top secret work that took place there during WWII & the vital part it played in the outcome of the war. It was so secret that much of this is still classified & some is still being revealed. The place was completely dismantled & everything including the complex electronic deciphering equipment developed there was destroyed soon after the end of WWII to prevent it falling into the hands of a potential enemy. It's hard to believe now but many of the people that worked there took their secrets to the grave & never revealed what they actually did there even to their spouses or close family.

It's a very interesting place for a visit if you get the chance & set in beautiful surroundings. http://www.bletchleypark.org.uk/ Near Milton Keynes so it's not diffcullt to find.

And another point, radio traffic amounted to operational info, which the codebreakers and analysts attempt to understand to put together strategic pictures of the enemy's intentions.  The Z Plan was a strategic document.  There's a big difference between the two.

Hagar,

point well made.

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A very interesting 'what if?" scenario. There are many other examples & towards the end of WWII counter-espionage was so rampant that it must have been very difficult to know quite what to to believe. I'm told that the German spy network in Britain was uncovered very early on & the spies were persuaded to cooperate by transmitting bogus information to their 'spymasters' throughout the war. In order for them to be believed some of the information in these messages had to be correct but it was apparently a very successful operation & possibly saved many lives. For it to work the actual spies had to transmit these messages themselves as each Morse code operator apparently has their own recognisable "signature" & any other operator would soon have been detected.

I seem to recall that the Germans recovered the plans of the Arnhem disaster intact from a briefcase left behind in one of the gliders but believed them to be a plant. They found it as difficult to believe as me that a senior officer would carry the detailed plans with him on the actual operation.

Well he was a bit Fuked in his dome!



A.