Even if no messages were read, other means wold still have made it possible to 'guess' enemy movements with a certain degree of success?
Does this go for Battle of Atlantic as well as it is hard to spot what goes on at 'ground' level?
Short answer is yes
Also, didn't the German 39-42/43 able to READ the Allies merchant codes? Which help them position the boats correct. BUT after 43, the Allies plug that intellegent hole. So Enigma or no Enigma isn't going to change that.
Now, what would be a interesting question is what if the GERMAN could cont reading the Merchant codes WITHOUT the allies reading Enigma. Could Donitz setup an intercept with one or both of the Queen troopship? They usually sail unescorted using their speed. BUT what if Donitz could position a boat exactly to get a shot off. Like the Allies did with the milk cows or the USN did to Japanese convoys(by reading Japanese messages).
What would the impact be when an ENTIRE US INF DIV personnel was lost.
Actually there were several months in 1942-43 when both the Naval Enigma source was blacked out to the Allies, and the Convoy code was being read by the Germans. I'll have to look up the exact dates dates, but the merchant convoy code had been penetrated from sometime in mid 1942, & not closed until late winter 1943. February I think. The advent of the four rotor machines aboard the submarines blacked out that source until a combination of the newest hyper fast decryption machines from the US & Turings attack programs were available.
What was the effect? First, some of the senior British leaders like Churchill were in a panic.
Second, convoy losses on specific convoys in the mid Atlantic soared.
There are two key phrases in that 2d result. "specific convoys" and "mid Atlantic". Some of the convoys running through the north Atlantic in the winter of 1942/43 never saw a torpedo hit. Owning the convoy code did not enable every one to be intercepted. There were so many convoys running the N Atlantic only a portion could be effectively attacked. Many of the attempts failed because a "intercept line" or wolf pack could not be set up fast enough. There were not enough submarines operational to effective attack every convoy. Fact is Donitz was only able to get the results he did that winter by concentrating nearly everything available in the North Atlantic. Only a few diversionary subs were sent to the mid or South Atlantic, or to other regions.
The other point here is "mid Atlantic", the famous Mid Atlantic Gap. This was the area the Allies could not cover with the PBY or other patrol planes made available to ASW mission in 1942. Those could not cover a wide swath in the mid Atlantic. However they could cover a considerable distance from the US/Canadian east coast, and the waters from Iceland, the UK, and Bermuda. There were aircraft as early as 1939 that could patrol over this region, but they were denied to Coastal Command or the RN through opposition from the USAAF & RAF leaders. They were able to deny the Very Long Range (VLR) aircraft to Coastal Command until early 1943.
IMPORTANT POINT HERE!!!
Where the Allies could cover with air ASW patrols the German subs could no longer operate effectively. That is from the autum of 1942 ASW air patrols from the US meant constant danger of attack from aircraft, followed by surface searches/attacks. Losses were too high to justify the declining ship sinking in the regions under air coverage. Around the UK this point had been reached in early or mid 1941. The Western & Southern Approaches to the UK ports were simply too dangerous for subs to patrol in. largely because of air patrol. Those transiting these waters to the Atlantic, or the Bay of Biscay from the French ports had to transit at high speed with minimal surface time at night. It had become too dangerous to make the transit in daylight or at economical cuirsing speeds to save fuel.
So just so you don't miss the critical point here; despite having the convoy code and the submarine encryption being blacked out the German sub fleet could not effective operate under Allied ASW air coverage.
When in the late winter when the Allies 'won' the Battle of the Atlantic it was not just blacking out the convoy codes, or breaking back into the submarine version of Enigma. Air coverage of the mid Atlantic was finally accomplished. That "panic" I referred to earlier on the part of the Brit leaders forced the issue. Churchill threw every bit of his political power into ensuring a small group of 24-30 VLR planes were in Coastal Commands hands. These were naval versions of the B24 bomber & flying from the UK and Iceland they closed the gap. Imeadiatly they sank several subs, more important they forced others to dive on a daily basis, and brought surface hunter teams onto the area. Abruptly the sub commanders had difficulty forming the wolf packs into intercept lines, no longer able to run on the surface without interfeance.
This air gap was closed in March 1943 when the VLR group started patrols. In a few weeks Doneitz decided the mid Atlantic battle was going badly & ordered the wolf packs withdrawn in early April. Losses had soared in march to unsustainable levels.
To belabor the point. Even with the naval version of Enigma blacked out the German submarines could not effectively operate in regions under Allied air ASW coverage. Losses were to high and cargo ships sunk too few to justify it.
I'd recommend both 'The Battle for the Code' by Montifiore & 'The Battle for the Atlantic' by Hughes & Costello. The former is the best source on the naval code war between the Brits & Germans. The second has detailed data for cargo ships and submarines sunk, including location for each calendar quarter. Those charts clearly indicate how the Battle of the Atlantic shifted about from year to year.
