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The originator of this operational technique was Luftwaffe officer Major Hajo Herrmann. A highly decorated bomber pilot, in early 1943 Herrmann was serving in a Luftwaffe staff position, studying operational practices and techniques, including counter-measures to the Allied bombing offensive gathering apace at the time.
In the spring of 1943, Herrmann proposed an experimental evaluation in the use of free-ranging day fighters (and to a lesser extent night fighters) at night to counter the increasingly destructive RAF night attacks. Fighter planes were not directed as in the "Himmelbett" (four-poster bed) technique using the tactical guidance of radar ground stations to the target, but rather interception was based (after radio guidance to the general area of the bomber stream) simply on the pilot's vision and own judgement; Wilde Sau "wild boar" was used as opposed to the Zahme Sau ("tame boar") method wherein an interceptor was guided by ground control.
In May 1943, the British acquired a Junkers Ju 88 R-1 night fighter (Werknummer 360043) when its crew defected to the Allied side and flew the aircraft to Scotland. The aircraft carried the initial "B/C" form of the UHF-band Lichtenstein radar, so its existence was revealed to the Allies; subsequently, RAF Bomber Command were approved to deploy a new form of window or chaff (aluminium strips) sized to jam the Lichtenstein B/C radar. This brought about the need to deploy new night-fighting methods that no longer relied solely on AI radar until the longer wavelength, VHF-band Lichtenstein SN-2 radar could be perfected and produced for use in German night fighters defending the Reich.
To this end, fighter pilots wherever possible sought to identify and intercept enemy bombers by sight. This was to be achieved by acting against the principle of the blackout, and Herrmann proposed that the attacked city was to produce as much light as possible. Being contrary to orthodoxy, this method was resisted by the city Gauleitern and not enforced. As a substitute, searchlights were used to illuminate the sky.
Initial tests using former flying instructors experienced in blind-flying techniques suggested the ideal weather conditions were when a certain (not too thick) lower level cloud cover prevailed, since then the bomber would be silhouetted against the back-lit clouds and the high-flying German fighters could easily spot their targets.
Since the Wilde Sau technique only worked if lighting was adequate, its application was limited to the immediate metropolitan city areas, as in most cases this was the only place where an assembly of sufficient searchlights was in place. It was therefore essential that the RAF's intended target was determined quickly. This was made more difficult to predict because the bomber stream often flew in a zigzag course across Reich territory.
To remove the threat from their own flak, aircraft were limited to certain altitude bands. This "ceasefire" was initially only practised in the Berlin airspace, and it showed that co-ordination of fire breaks was problematic. As night-flying aids in a day fighter were rudimentary, an accordingly elaborate system of visual aids to navigation was established, encompassing light beacons, searchlight patterns, flak firing combinations of various tracer colours through the clouds, and parachute flares.
The firestorm bombing of Hamburg proved disastrous for the Luftwaffe, after the Allies' first use of window effectively knocked out the Himmelbett radar defence system. As a result, every other promising measure of preventing such a recurrence was considered.
Hermann's original experimental unit was, therefore, rapidly expanded into a full Jagdgeschwader, Jagdgeschwader 300, which used the Wilde Sau tactic for the first time on the night of 3/4 July 1943, when 653 RAF aircraft attacked Cologne. The German fighters, taking advantage of the illumination from searchlights, target indicator flares, and ground fires, claimed 12 aircraft shot down, but had to share their claims with the antiaircraft batteries which also claimed the downings.
The employment of this procedure was most successful on the night of 23/24 August 1943, when Berlin was attacked. The Wilde Sau aircraft, under the personal leadership Geschwaderkommodore Hajo Herrmann, claimed 57 aircraft brought down. Herrmann received the Oak Leaves to the Knight's Cross for this action.
Limitations of this method of attack
If the cloud ceiling at the time of the attack were too high, restricting the lighting effect, the optical conditions were insufficient to apply Wilde Sau. The success of the attacks was also lost with the onset of bad winter weather in late autumn 1943, when wastage through accidents and icing soared. German pilots were always at risk from their own antiaircraft fire. Even if Wilde Sau were also partly accomplished by twin-engine night fighters, the bulk of the action was carried out by conventional day fighters borrowed from the day Jagdgeschwaders. This double load of day and night operations and the resulting erratic maintenance schedules meant fighter serviceability rates dropped drastically.
The specially established 30. Jagddivision consisting of Jagdgeschwader 300, 301 and 302, all named Wilde Sau, applied this technique. Also attached to 30. JD was III./KG 3 which was tasked to fly above the bomber stream and illuminate it with flares.