Reconnaissance aircraft observe hostile airspace to identify enemy’s strength furnishing assets (troops, factories, depots, ships, etc.), their location, disposition, & movements. Intelligence staffs assess the information to reveal their relative strength/importance and based on it, they compile lists of targets for attack, classified by importance and category.

Recce airplanes also fly to recently attacked targets to assess damage, check weather patterns, and carry out signal intelligence missions.
This information is critical for operational commanders (who decide which targets to attack, when, and how) and much effort is devoted to these missions.
A good reconnaissance aircraft needs the range to penetrate the target zone, and the performance to snap the needed pictures and return to base in one piece. For recce aircraft, the main attributes are high speed or altitude, adequate range (to reach the target), and payload (for the cameras).

During the Battle of Britain, the Germans employed Do 17s, Ju 88, Bf 110, and He 111 in specialized reconnaissance units. All these aircraft proved vulnerable in British skies. The British initially utilized the Blenheim but it proved vulnerable and by early 1940, they used the Spitfire successfully.
The Luftwaffe had a High Command Reconnaissance Gruppe that included specialized aircraft like the Ju-86P (pic).

This aircraft had the characteristic that it could fly well above any other aircraft of the time (38,000 ft). It possessed a pressurized cabin for the crew (of two), and two double-supercharged diesel two-stroke Jumo 207 engines (1000 hp each with Nitrous Oxide). It was equipped with two large 75cm Zeiss cameras, each weighing 70kg.
On 18 Aug 1940, at 1:25PM a Ju 86P flew over Portsmouth in an NW direction leaving a clear condensation trail, so it was quite visible. A flight of Hurricanes from 43 Sqn (Tangmere) was sent to intercept but they failed, despite the intruder’s low speed (160 mph). The Hurricane simply lacked the ceiling to reach the intruder.
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