Many historians of the Normandy campaign note that the defenders, although aware that an invasion must come, were nevertheless caught off guard when it actually did. None that I have read goes far into the question, beyond noting the success of Allied deception measures. In The Longest Day (1959), Cornelius Ryan takes an extreme position:
… the Germans remained blind … only a few planes had been sent over the embarkation areas in the preceding weeks, and all had been shot down.
Brief investigation shows that Luftwaffe reconnaissance aircraft were not in fact dropping like flies over Southern England in Spring 1944 and Max Hastings (Overlord, 1993) makes a more nuanced observation:
Germany’s critical weakness on the Channel coast in the spring of 1944 was her blindness. The Luftwaffe had lost not only its strength but its will. Despite the difficulties posed by Allied command of the air, some measure of air reconnaissance might yet have been possible given real determination by the German airmen.
Although his source for this is not clear, Hastings pretty much hits the nail on the head. I would only differ with him about strength — Luftflotte 3 had quite a range of overland reconnaissance assets in Northern France and the Low Countries. Facing the Channel and North Sea in May were:
The fighter types, the Ju 88 S/ T series and the Ju 188 had the potential to operate over the British mainland, by day or night as appropriate, and return home. Undoubtedly a sustained effort would have incurred losses but the Luftwaffe did not hesitate to sacrifice men and machines where this seemed necessary to achieve a desired result.
The Bf 109 Staffeln carried out similar tasks, despite two being designated »Nah« (short-) and »Fern« (long-range) respectively. From the available information, their equipment did however differ in detail, although the workshops (notably Guyancourt, SW of Paris) were not always able to meet their precise requirements. NAG 13 received few G-5 (pressurised) variants or AS-powered variants and its aircraft normally carried standard fighter armament along with Rb 12.5 cameras, suitable for photography from 500–5000 m. When the newly-formed 3. Staffel came on the scene at the end of April, all but one of its machines were Bf 109 G-8 in the 710 000 series with full armament and MW 50 boost.
The Luftwaffe did not generally go as far as the RAF in converting fighter types into “pure” reconnaissance machines. Rather than stripping weight from their Bf 109s, as the British did with PR Spitfires, they made them heavier than the standard fighter model. Reconnaissance Messerschmitts bore a significant weight penalty: an Rb 50/30 camera with fittings and film magazine weighed 72 kg while the MW 50 system added another 63 kg. Standard armour, guns and ammunition totalled 270 kg although removing the two MG 131 and their ammunition (as 4. and 5.(F)/123 generally did) would save around 44 kg.
The 5.(F)/123’s “ideal” machine seems to have been a Bf 109 G-5/AS with just a single MG 151/20 cannon, MW 50 and an Rb 50/30 camera (offering good results at 6000 m or more). The Staffel appears to have been rebuilding since 30 March, when it had consisted of:
5 Bf 109 G-4, 2 Bf 109 G-5, 2 Bf 109 G-6 and 2 Fw 190 A-5
1 Bf 108 and 1 Fi 156 (communications aircraft)
At that point, four of the Bf 109s and one Fw 190 had been absent or unserviceable while only three pilots had been ready for operations (one was conditionally ready, one on leave and seven detached).
The 4. Staffel seemingly had many more G-6 sub-types, similarly equipped, but both units ended up flying a mixture and it appears that they were phasing out their Bf 109 G-4s during the Spring.
There were a few Fw 190s distributed throughout NAG 13 and FAG 123 but no definite reports (in the sources I have so far consulted) of their being used over the Channel or British Isles during this period although they had flown frequently in March. The 4.(F)/123 gave up its last two in April while the 5. Staffel had some on strength until August. Over the Summer NAG 13 seems progressively to have concentrated its Focke-Wulfs into its 2. Staffel while withdrawing that unit’s Bf 109s.
On the quality of German photography, S/L David Linton of the Allied Central Interpretation Unit at RAF Medmenham had this to say, based on captured examples:
So let us look now at what the German units actually did.
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