Employment of German AAA, WWII Tactical and Technical Trends, No. 35, October 7, 1943 (Lone Sentry)

The development of modern antiaircraft artillery as compared to all other types of artillery probably has resulted in the most advanced type of weapon in this category. Because of its ballistic qualities, automatic controls and the technical excellence of the instruments used, these weapons have been of great tactical use in the hands of the enemy.

The following article taken from AFGIB (Air Forces General Information Bulletin) September 1943, describes some general principles underlying the methods of operation of these guns and also takes up the question of the performance characteristics of the various German types.

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The term "Flak," as related to German antiaircraft, is an abbreviation for "Fliegerabwehrkanone," which means antiaircraft gun. However, in common parlance of the British and our own forces, Flak generally means the fire from such guns rather than the guns themselves. This usage is exemplified in such statements as that "Flak was intense and accurate at X feet," etc.

Like fighter aircraft, which constitute the other major hazard to operation of our planes over enemy territory, antiaircraft guns and gunnery have been constantly improved in their capabilities and effectiveness during the present war. This article attempts to present a general picture of the present status of German equipment.

German guns in common use against aircraft may conveniently be considered under three main classifications, namely: (a) machine guns and small arms; (b) light antiaircraft, consisting of automatic weapons; and (c) heavy antiaircraft, firing high explosive projectiles equipped with variable time fuzes. Each of these categories has its own zone of employment and major effectiveness. Assuming that the target aircraft flies within the horizontal range of the weapon, the altitude of the target mainly determines the effectiveness of each category of weapons for the particular case.

Aircraft flying over German-held territory at very low altitudes are apt to encounter heavy machine gun fire; and when over troops, to be also the target for everything available in the way of small arms as well. (see Tactical and Technical Trends No. 30, p. 6) It is standard German practice to send up a hail of bullets from every sort of weapon that can be brought to bear, and the concentration of fire from troop columns has been described as very heavy indeed. The German machine gun most commonly used is the air-cooled 7.92-mm (0.31 inch) gun. It has a maximum vertical range of about 8,500 feet, but the slant range for tracer observation is only about 3,000 feet and fire is effective only to about 2,400 feet. The rate of fire for short bursts may be as high as 1,100 rounds per minute, and ammunition for the antiaircraft role is usually fed in the ratio of one tracer, two armor piercing, and two incendiary bullets.

a. Safest Flying Procedure

For aircraft which must fly well within the effective range of machine guns, it is generally considered that the safest procedure is flight at the minimum possible altitude--preferably 50 feet or less--taking every possible advantage of cover in the shape of terrain features, including hills and valleys, trees, and buildings. Speed, surprise, and evasive action are highly important, as is also the direction of the aircraft's attack. For instance, straight, lengthwise flight over a troop column is likely to be very unhealthy. It is evident that the gunner's problem is most difficult when he has the target in view for the shortest time, and must traverse his gun rapidly to follow it, allowing for corkscrewing changes of course and altitude by the plane.

German light antiaircraft guns--automatic weapons--include a 20-mm cannon corresponding to the Oerlikon or Hispano-Suiza; a 37-mm, somewhat similar to our gun of that caliber; a 40-mm Bofors; and a dual purpose 50-mm. The latter two are less commonly encountered, as some 70 per cent of the automatic weapons are 20-mm and some 20 per cent are 37-mm. In the antiaircraft role, these weapons fire high explosive tracer shells equipped with percussion and self-destroying fuzes.

The 20-mm has a maximum horizontal range of 5,230 yards and a maximum vertical range of 12,500 feet, However, the shells normally do not reach this altitude, as with 6-second self-destroying tracer ammunition they explode at about 7,200 feet. The effective ceiling for accurate engagement is considered to be about 3,500 feet, The theoretical rate of fire for the Model 30 is 280 rounds per minute, and for the Model 38 is 450 rounds per minute. Practically, these rates reduce to about 120 rounds and 200 rounds, fired in bursts of up to 20 rounds.

The 37-mm has a maximum horizontal range of 8,750 yards, and would have a maximum vertical range of 15,600 feet, except that the 14-second tracer ammunition self-destroys at about 13,800 feet. With 7-second tracer, the shells self-destroy at about 9,200 feet. As with the 20-mm the effective ceiling for accurate engagement is less than these figures, being about 5,000 feet. The theoretical rate of fire of the 37-mm weapon is 150 rounds per minute, which reduces in practice to about 60 rounds per minute for cartridges loaded in clips of 6 rounds each. High explosive shells of both the 20-mm and the 37-mm have an instantaneous percussion fuze which functions on impact.

The usual fire control equipment for German light automatic weapons is a gunsight with a computer mechanism on the course and speed principle, together with a separate stereoscopic range finder. Other sights are used in which the necessary deflections in azimuth and elevation are automatically calculated by an electric control mechanism that operates when the traversing wheels are moved. Forward area sights are attached for firing at very close range when a high rate of traverse of the weapon is necessary.

The fire is corrected by visual observation of the paths of the tracers. The fact that such observation is correct only for the earlier and flatter portion of the trajectory accounts for the previously mentioned reduced figures for "effective" range. Beyond the "effective" ranges, the probability of a hit drops off rapidly.

German heavy antiaircraft guns, like our own, fire high explosive shells equipped with time fuzes. These explode after a chosen time interval for which the fuze can be set, and consequently at a definite range. The shell fragments are projected outward from the burst at high velocity, and this produces a certain "lethal area," larger or smaller according to the size of the shell.

The principal German heavy antiaircraft guns are as follows: (a) the 75-mm, corresponding to our 3-inch; the 88-mm, which somewhat corresponds to our 90-mm; the 105-mm, the 128-mm or 5 inch; and the 150-mm or 5.9 inch. About 65 per cent of the German heavies are 88-mm, and about 20 per cent are 105-mm. The 75's, 128's, and 150's are thus comparatively rare, and in planning high level air operations it is usually sufficient to make estimates on the basis of capabilities of the 88-mm and 105-mm guns.

In the same way that the self-destroying tracer reduces the theoretical maximum vertical range of light automatic weapon shells, so does the limitation of the time fuze used reduce the theoretical maximum vertical range of heavy antiaircraft shells. The maximum vertical range of the 88-mm, theoretically 35,700 feet, is thus reduced to a ceiling of 32,500 feet for maximum time setting of the fuze employed.

Corresponding figures for the 105-mm are 41,300 feet and 37,000 feet. The lethal radius of burst, for the 88-mm is considered to be about 30 feet, and the practical rate of fire 15 rounds per minute. For the 105-mm shell, lethal radius of burst is about 50 feet, and the practical rate of fire from 8 to 10 rounds per minute.

b. Capability of Heavy Antiaircraft

In order to get a picture of the general capability of a heavy antiaircraft gun, it is useful to consider the line traced by the shell bursts if we fire, with maximum fuze time setting, a series of shots aimed toward the same compass point but at successively greater angles of elevation above the horizontal. The first shell, fired at a low angle, will burst far out from the gun horizontally, but at low altitude. Each successive shell, fired at a higher angle, will burst less far out horizontally and at a greater altitude. It is evident that if we join the successive shell bursts by a continuous line, we get a rounding curve extending upward from the maximum horizontal (fuze) range to the maximum vertical (fuze) range.

If we picture this series of shots as being repeated with different compass-point aimings of the gun, it is evident that we get a series of exactly similar curves, which all together define for us a sort of rounded, umbrella-like envelope in space, over the gun,

This imaginary "umbrella" is the "limiting envelope" for the particular gun. It is evident that an airplane flying anywhere under this umbrella is within range of the gun, and that an airplane outside it is not within range.

If we imagine this "limiting envelope" to be cut by horizontal slices at various altitudes--5,000 feet, 10,000 feet, etc.--we obtain a series of circles, one for each height. These are the "effective gun circles," each applying to its particular altitude. An airplane flying at any particular altitude comes within gun range when it touches on or is inside the "effective gun circle" for that altitude.

[Ceilings for WWII German Flak Guns]

c. Fire Control Methods

The Germans use three main methods of fire control, namely: (a) continuously pointed fire, with director control; (b) predicted concentrations by plotting; and (c) barrage fire.

In continuously pointed fire, operators for each battery independently follow the target through telescopes. Its altitude is inserted from a range finder, and the necessary calculations are made mechanically by the director, for aiming the gun at a point in space where the shell and the airplane will arrive simultaneously--provided the airplane does not change course, altitude, or speed on which the director bases its prediction. Appropriate evasive action therefore consists of changes in course and height, at intervals determined by the necessary time for prediction of aim and flight of the shell. Due to the longer time of flight of shells, and the shorter period during which the gun can engage, the effectiveness of this type of fire decreases rather rapidly at the higher altitudes. The effective ceiling for this type of fire is less by about 6,000 feet than the maximum fuze range of the shell, as indicated by the diagram.

Predicted concentrations can be fired to the full height allowed by maximum fuze time setting. For this type of fire, a plot of the aircraft's course is made in a central control room; and as soon as its intended course on its bombing approach can be predicted, necessary data are calculated for a future point of its arrival in the sky. Each gun battery, utilizing the basic data, makes its own computation for this predicted point, and each battery fires a salvo so timed that salvos of all the batteries burst simultaneously at the predicted point. Sometimes second and third salvos are fired immediately on the same data.

This method requires that the aircraft be flying reasonably straight and level for about 90 seconds before reaching the predicted point. Evasive action is indicated up to the actual beginning of the bombing approach, which should be as short as consistent with accuracy of bombing. Subsequent concentrations against bomber formations passing through the same predicted point may be fired in a much shorter time since the initial plotting already has been done.

Barrage fire, as the name indicates, depends on the placing of a barrier across the probable course of the aircraft. A geographical or fixed barrage is fired by all guns within range into a certain sky volume or box, usually just outside the expected bomb release line of the aircraft. If the barrage is properly placed, the aircraft must fly through the bursts in order to bomb the objective. It is obvious that the gunners should be kept uncertain, up to the last possible moment, as to the intended objective and the direction of the bombing approach.

In a short article of this nature, only highlights can be touched upon. Detached studies of antiaircraft gunnery have been made, which go thoroughly into the effectiveness of each category of weapons over the appropriate zone of fire. Their findings are of great practical value to all who fly on combat missions. The recommendations made with respect to evasive action and protective measures during flight over enemy territory derive from the combined experience and best thought of competent authorities. Careful attention to such studies, and thorough understanding of their precepts, will pay dividends in added safety.