NFG here!

[Aktungbby]

Johnnycat! required reading is the two volume 'Hitlers U-boat War '. & What's essential is to understand is that only a small number of U-boat aces accounted for most of the tonnage and...the U-boat War which so worried Churchill is a lost cause from the getgo; WWI technology applied to WWII resulting only 3 to 5% of allied shipping losses overall and 75 % losses for the undersea branch of the Kreigsmarine...a study in maritime strategic futility!

 

By the end of the war, although the U-boat arm had sunk 6,000 ships totalling 21 million GRT, the Allies had built over 38 million tons of new shipping.
The reason for the misperception that the German blockade came close to success may be found in post-war writings by both German and British authors. Blair attributes the distortion to "propagandists" who "glorified and exaggerated the successes of German submariners", while he believes Allied writers "had their own reasons for exaggerating the peril".
Dan van der Vat suggests that, unlike the US, or Canada and Britain's other dominions, which were protected by oceanic distances, Britain was at the end of the transatlantic supply route closest to German bases; for Britain it was a lifeline. It is this which led to Churchill's concerns. Coupled with a series of major convoy battles in the space of a month, it undermined confidence in the convoy system in March 1943, to the point Britain considered abandoning it, not realising the U-boat had already effectively been defeated. These were "over-pessimistic threat assessments

 

Blair concludes: "At no time did the German U-boat force ever come close to winning the Battle of the Atlantic or bringing on the collapse of Great Britain''.