NOTES ON THE WAR NEWS

Evening Post, Volume CXXX, Issue 99, 23 October 1940, Page 10

NOTES ON THE WAR NEWS

"FLAK" .& ITS USES

ANTI-AIRCRAFT GUNS

TYPES AND METHODS

Every Royal Air Force pilot who returns from a raid over Germany probably makes some reference to anti-aircraft fire in his report. But he will call it "flak." He may say that flak was heavy or that it was light, that it was accurate or inaccurate, moderate or intense, or even that there wasn't any. The word he uses comes from the German initials FI.A.K., which stand for "Flieger Abwehr Kanone," or "the gun that drives off raiders." The New "Archie." "Flak" today supplies the place of "Archie" in the World War, but of course it stands for a much more complicated business than the "Ack-Ack" fire with which the men of the Royal Flying Corps were familiar. It is closely studied in Britain, and the Intelligence Department at the Air Min,istry recently issued a "guide to flak" for the benefit of those concerned.

This guide shows the range, calibre, weight, and type of shell used by the Germans and the rate of fire of each kind. There are two principal kinds, light and heavy. "Light" flak is from guns of a calibre of between threequarters of an inch (20 millimetres) and two inches (47 millimetres). The weight of shell rises from less than half a pound to three and one-third pounds in the case of a 47 mm. gun. The rate of fire decreases, as might be expected, and the range increases, with the increase in the size of the gun.

For example, the German 20 mm. gun fires about 160 rounds a minute, up to 7000 ft, while the 47 mm. fires 25 rounds a minute to a height of more than three miles. Tracer Shells Used. There are light guns firing tracer shells which burst on impact and have self-destroying detonators. They exr plode in the air even if they miss their [ target, and so cannot fall back to the ground and burst there. The heavy guns do not fire tracers but use timefused shells, and the class includes the 75 mm. (3in) gun which throws shells 20,000 ft at the rate of 15 a minute and the 105 mm. (4in) gun which will send ten 321b shells a minute up to 30,000 ft.

There is a difference in fire control between the light and the heavy guns. Light gun-fire is directed by a speed and course sight; heavy is controlled by a predictor, a complicated instrument which needs eleven men to work it and which provides the gunner with the data necessary ifJhe is to hit,his target. This instrument, however, makes it possible for the shell to hit the target only, if, in the interval, between the firing of the gun and the arrival of the shell at the point of prediction, the aircraft has not changed speed, height, or direction. Normally an aeroplane under fire from flak would constantly change at least one of these three. At night or in cloud, flak fire can b« directed by sound locators, but thi3 fire is naturally much less accurate than visual shooting. British Guns Better. Britain's anti-aircraft batteries have guns equal to or better than the German. Since the "Battle of Britain" began our anti-aircraft batteries have brought down many Nazi raiders, whereas British aircraft frequently return home after flying through a heavy flak barrage and suffering no damage at all.

In general anti-aircraft guns have not fulfilled the prophecies of some military experts, who thought that four out of five enemy planes would be shot down by fire from the ground, and not by fighters as was the case in the World War. This belief received some colour from reports coming out of Spain, which declared that about half the machines lost there were the victims of the German-operated batteries which were sent there to aid General Franco. The Three Types. Today the flak of all countries ia maintained by three types of gunsfixed weapons, semi-mobile ones or those on mobile mounts of the kind recently reported to be placed in' Berlin streets. The great majority are of the last-mentioned variety. A feature of the anti-aircraft gun is that it makes a splendid anti-tank weapon because it can be depressed as much as 10 degrees below horizontal. The Germans made this discovery in Spain.

The largest and most weapons in use by any Power are said to fire up to 40,000 ft (about li miles), though they are not expected to ba us^d above 35,000 ft. The largest guns are hand-loaded, shell by shell, and so is the 3in gun, which reaches its rapid rate of fire (about 30 rounds a minute) because of the relatively light and easily-handled projectiles used. Many of the medium and some of the larger guns are designed for semi-automatic fire and can use clips or magazines.

i The typical anti-aircraft gun has an elevation of about 85 degrees, and swings round in a complete circle, thus i covering the whole sky save for a small spot directly overhead. The fact that the guns have to seek their targets in the sky with shells which have a minimum curve means that high velocities are needed for their projectiles. Ths average muzzle velocity of an anti-air-craft gun is about the same. as a rifle bullet, 2700 feet per second. Still higher velocities could be obtained, but it has been found that the guns tend to overheat in-such cases and this reduces their rate of fire. Electric Control. Most of the smaller guns are aimed and handled by individual crews independently of other weapons of th» same type, but for larger guns, of 3in and upward, electric control is often j used. Under this arrangement the guns are laid and fired in batteries of four or more. The device known as a predictor is first of all a range- | finder, employing old methods to deterimine distances by measurements of ! angles, and converts the distance bei tween the plane and itself into altituda land automatically transmits the data to another device known as a director. The director determines the firing data.

Watching an anti-aircraft battery in action one sees the guns move slowly towards the portion of the sky where the target is expected to be, just as a hunter moves his shotgun ahead of birds in the air. The predictor automatically gives all the guns of the battery the same information at the same time. The gun crews, in the electri-cally-controlled batteries, merely hava to keep the guns set on the data received and attend to the loading. The object is not necessarily to hit tha raiding plane, but to get a shell-burst as close as possible. Sixty yards away is considered well inside the danger zone for tbjQ airmen, -