Why was D-Day successful?

Transcript
Extract from a German intelligence report that was intercepted by British intelligence

Catalogue ref: HW 1/2784

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PAGE FOUR.

CX/MSS/T183/84 (CONTINUED).

Enemy mining from the air remained lively with Schwerpunkt [the main emphasis] off submarine bases, Lezardrieux and against Channel Island narrows. Agents' reports, apart from a plethora [excess, huge number] of landing dates which mainly point to the first half of May, yielded no special information.

C[ommander] in C[hief] West appreciates the situation as follows:

Invasion-preparations by the Anglo-Americans in the English Motherland are completed. Despite the fact that visual and photo recce [reconnaissance] has not yet been able to include the whole of the English south coast, the observed concentrations of landing shipping space, especially in the area north of the Isle of Wight (Portsmouth-Southampton), nevertheless give a clear picture of a main concentration defining itself in that area. Tonnage of shipping space for landings which has so far been observed can be assumed to be sufficient for 12 to 13 divisions (without heavy equipment and rear elements) for fairly short sea-routes.
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