After early domination of the seas by German U-boats, Bletchley desperately needed to end the intelligence blackout. Through a series of dangerous raids on German U-boats, a German Naval codebook was captured, thus making the Naval Enigma transparent. Finally, Ally convoys could evade the deadly German vessels and British destroyers could
go on the offensive. The Allied powers went to great lengths to not raise suspicion in Germany that their sacred Enigma machine was compromised. Fortunately for Bletchley, Germans were far too confident in the strength of their encryptions.
Although the Allies were now aware of the locations of numerous U-boats, they had to be careful not to attack all of them because this would warn Germans that they could no longer trust their communications. Therefore, they were careful to prudently attack and never risk destroying too many enemy ships at once. In one case, Bletchley became aware of a numerous amount of German tankers and decided to sink most of them, but not all as to not raise suspicion. The British destroyers successfully sank the ones they were supposed to, but then spotted the remaining German supply ships and sunk those as well because they did not know about this situation. Fortunately for the Allies, when the Germans realized about their lost ships, they thought of it as a misfortune because their Enigma was unbreakable. If the Germans had had less confidence in their encryptions, it is possible that they could have stopped the amount of information they were feeding the Allies, or even have used it against them.