German Searchlights, WWII Tactical and Technical Trends, No. 27: June 17, 1943 (Lone Sentry)

In World War I, searchlights were occasionally used to locate intruding aircraft, but they were not sufficiently coordinated with air defense to cause enemy pilots much concern.

In the present war, the use of searchlights in belts, clusters, and circular groups is a part of the complex defense system that the Germans have devised to offset the effectiveness of massed assaults by Allied bombers. The organization of German searchlights and guns is on a regional basis. Each region controls the permanent flak defenses, fighter units, reporting system, balloon barrage, and civil defense. The Germans have organized their searchlights well and use them effectively for illuminated target fire with their gun defenses (see Tactical and Technical Trends, No. 6, p. 6).

Searchlight belts were first seen in Germany in March, 1941. The most extensive belt had an enormous number of searchlights, but no flak. It was solid light and extended 10 to 20 miles in depth, its sole purpose appearing to be the direction of GAF night fighters to the enemy bombers. This belt was discontinued in May, 1942, probably because it was not sufficiently effective to justify such a heavy concentration of lights and operating personnel. However, searchlights which were employed in cooperation with flak had obtained some considerable measure of success, as they tended to impede accurate navigation of Allied planes and subjected their crews to considerable strain en route to and from their objectives. Concentrations or groups of 10 to 15 and 20 to 40 lights were found in fighter-protected areas, on the approach lanes to important targets, and in gun-defended terrain. Batteries of two or three lights, set 25 to 75 yards apart, have also been seen.

Last November, searchlights appeared in the form of circular groups of 15 to 30 lights, the majority of which were controlled by master lights. The master light, which has a bluish tint due probably to the small divergence of beam and the very high current used, picks up the aircraft, and then the cone of light produced by the group centers on the master light and moves with it. The accuracy of the master light suggests that it is controlled either by some form of radio detection device or by a particularly efficient system of sound location. However, unless the remainder of the lights in the group promptly expose and illuminate the plane, they can often be avoided by an immediate change of course or speed. Each cone unit is coordinated with a larger number of antiaircraft guns. Spaced between the various cone groups, there are individual lights searching for the planes. When a plane is in focus, other beams join the first and hold the aircraft until the cone can pick it up. At heights up to 18,000 feet, 15 to 30 cones give very good illumination, and they are particularly effective in directing flak between 5,000 and 14,000 feet.

Until the aircraft is firmly held, searchlights are either radio-detector-controlled or controlled by sound. If the searchlight follows a rapid change in course, it is usually radio-detector-controlled. If it gropes for the aircraft and cannot follow rapid changes, it is probably sound controlled. Many of the lights now search independently. When the plane is spotted, searchlights using visual remote control concentrate on it to form a cone.

Searchlights used independently of flak have several purposes. They silhouette planes so that night fighters can see them more easily; indicate the track of attacking planes to night fighters, antiaircraft units, and searchlight-cone groups; dazzle bomber crews so they cannot see fighters or targets; hide targets from view by concentrating a cone of light over them; and counteract the effect of parachute flares by placing a cone of light under the descending flare.

A single searchlight may indicate the track of an Allied bomber by pointing at it vertically and then moving horizontally in the direction of its course. It may also focus on a point in advance of the bomber's estimated course, and, perhaps, wave in the direction of flight. Circles are described around the plane to indicate its presence and track, and to invite other individually controlled searchlights to focus on it until it can be transferred to a cone. Successive pairs of lights, directed one on each side of the plane and forming a lane, may indicate the path of the bomber. Sometimes a wall may be formed to silhouette the attacking plane for night fighters flying at the same level. The projection of light patches on a cloud below the aircraft silhouettes them to overhead fighters and a cone may similarly be used as a background.

The dazzle effect of the light is greater in a haze than in clear weather. Lights may sweep horizontally to dazzle crews, making it difficult to see the target. A single beam cannot produce a "dazzle" effect except at short range, but concentration of several beams can cause acute difficulty to the pilot or bombardier. It can occur only when the aircraft is directly illuminated, and, although effective up to 15,000 feet, is most pronounced between 2,000 and 4,000 feet. "Glare" can be very effective on nights where there is considerable, ground or industrial haze. The searchlights sometimes project beams at a low angle of elevation onto the haze, producing a pool of light over the target and making identification difficult for bombing crews. Both dazzle and glare interfere with night vision, make the location of targets difficult, lessen bombing accuracy, and help night fighters to approach the enemy bombers unobserved.

A recent analysis of searchlight operations led to the following conclusions: German antiaircraft defenses rely mainly on unseen methods of control but augment their fire by visually controlled guns, using searchlights only when there is little or no cloud. Among aircraft coned by lights for more than 20 seconds (and therefore probably engaged visually), the percentage damaged has been about twice as high as among planes illuminated for a shorter period. There was no evidence that those coned for more than 20 seconds were subjected to more intense antiaircraft fire than others. The risk of being illuminated by searchlights seemed to be about the same at all bombing altitudes (6,000 to 20,000 feet). On one occasion when conditions were favorable for searchlights, there were 70 to 80 bombers over a target at one time and they were effectively coned (i.e., for more than 20 seconds) at the rate of about one per minute. Heavy antiaircraft fire in coordination with searchlight cones is extremely accurate and destructive. Once a cone centers on a plane, it ignores all other aircraft and proceeds methodically to direct the destruction of the one it has caught.