To argue that ULTRA was decisive in the Atlantic campaign you would first have to accept that there was a chance that the Uboats were going to be successful in starving Britain out of the war, now while I have no doubt there were dark moments in the Atlantic war that scenario was never going to happen.
I never suggested that Britain would be starved out, as far as I am aware no one did. Yes there were quite a few dark moments during the U Boat campaign, which I assume worried Churchill.
Therefore ULTRA only affected the timeline of the campaign not it's outcome hence it was not decisive..
I assume you are still talking about the U Boat campaign and not the other campaigns that were won like North Africa and Italy thanks to ULTRA.
To quote Prof. Dr. Jürgen Rohwer as posted by Der Alte
I am sure that without the work of many unknown experts at Bletchley Park…the turning point of the Battle of the Atlantic could not have come as it did in May 1943, but months, perhaps many months, later. In that case the Allied invasion of Normandy could not have been possible in June 1944,
and there would have ensued a chain of developments very different from the ones which we have experienced. Now I wonder what those developments could have been and how strange most historians don't agree with you and your mate?
From
http://www.militaryhistoryonline.com/wwii/atlantic/enigma.aspx
The introduction by Donitz, from late 1940 onwards, of "wolf-pack" tactics, gave the Enigma codes still greater importance. In order to rendezvous U-boats had to signal their positions to Donitz's operations room. If these messages could be deciphered, it would be possible to divert convoys away from known ambushes. But it was becoming clear that little progress could be made without further captures of enemy material, itself a hazardous procedure, for if the Germans became aware that Enigma material had fallen into enemy hands, their whole cypher system might be changed.
On March 4th 1941, during a Commando raid on the Lofoten Islands off Norway, the Royal Navy captured the German trawler Krebs, along with two Enigma machines and the current settings for use in home waters. This allowed another partial breakthrough, allowing some messages to be read. Donitz, whilst concerned by increased British naval successes, was assured by his cypher experts that Enigma was unbreakable, and tended to suspect that the problem was due to increasingly effective tracking by means of HF/DF signals.
It was in the spring of 1941 that Britain made an important breakthrough in the battle for Enigma. Harry Hinsley, one of the Bletchley codebreakers, realised that the network of German weather and supply ships currently operating in the Atlantic, would carry code information.
The problem lay in capturing some of these without betraying to the enemy exactly what was going on.On May 7th, in a highly secret operation, Royal Navy ships intercepted and captured the weather ship Munchen, seizing the code books to be used in June. Two days later, in one of the most dramatic episodes of the war at sea, depth charges fired by British destroyers forced to the surface U-110, whose commander, Lemp, had sunk the liner Athenia on the opening day of the war. Believing his vessel to be sinking, Lemp failed to destroy either his Enigma machine or its codes. Whilst sailors opened up on the U-boat crew with rifles and machine guns to panic them, and prevent any returning below deck, HMS Bulldog closed in and boarded U-110. Both machine and codes were seized. Lemp was not among the survivors of the U-boat crew, and once again the extent of their success remained a carefully guarded British secret.
The introduction by Donitz, from late 1940 onwards, of "wolf-pack" tactics, gave the Enigma codes still greater importance. In order to rendezvous U-boats had to signal their positions to Donitz's operations room. If these messages could be deciphered, it would be possible to divert convoys away from known ambushes. But it was becoming clear that little progress could be made without further captures of enemy material, itself a hazardous procedure, for if the Germans became aware that Enigma material had fallen into enemy hands, their whole cypher system might be changed.
On March 4th 1941, during a Commando raid on the Lofoten Islands off Norway, the Royal Navy captured the German trawler Krebs, along with two Enigma machines and the current settings for use in home waters. This allowed another partial breakthrough, allowing some messages to be read. Donitz, whilst concerned by increased British naval successes, was assured by his cypher experts that Enigma was unbreakable, and tended to suspect that the problem was due to increasingly effective tracking by means of HF/DF signals.
It was in the spring of 1941 that Britain made an important breakthrough in the battle for Enigma. Harry Hinsley, one of the Bletchley codebreakers, realised that the network of German weather and supply ships currently operating in the Atlantic, would carry code information. The problem lay in capturing some of these without betraying to the enemy exactly what was going on.
On May 7th, in a highly secret operation, Royal Navy ships intercepted and captured the weather ship Munchen, seizing the code books to be used in June. Two days later, in one of the most dramatic episodes of the war at sea, depth charges fired by British destroyers forced to the surface U-110, whose commander, Lemp, had sunk the liner Athenia on the opening day of the war. Believing his vessel to be sinking, Lemp failed to destroy either his Enigma machine or its codes. Whilst sailors opened up on the U-boat crew with rifles and machine guns to panic them, and prevent any returning below deck, HMS Bulldog closed in and boarded U-110. Both machine and codes were seized. Lemp was not among the survivors of the U-boat crew, and once again the extent of their success remained a carefully guarded British secret.
The effect of the improved flow of intelligence information was apparent during the second half of 1941. Increasing numbers of convoys were being diverted away from waiting U-boats. In July, for example, not a single convoy was sighted by the Germans over a period of three weeks, and during July and August monthly sinkings went below 100,000 tons, the lowest for over a year.
As lljadw has pointed out even during the early days when Uboats were sinking ships faster than Britain was building them Allied tonnage never decreased due to the influx of captured/impounded ships and the acquisition of ships from conquered countries such as Norway, Poland and Holland.
I pointed out that little gem that Britain was losing ships faster then they could be built which your mate refuted until I posted proof.
There were simply not enough Uboats at the beginning to win the campaign and by 1943-1944 when there were enough Uboats it was too late to change the outcome due to Allied technical advances.
I agree advances such as ship borne radar also became vital in the Battle of the Atlantic, many U Boats were sunk because of it.
