ANTI AIRCRAFT GUNNERY

The problem of attacking flying machines by gun-fire from the ground exercised ingenuity of most alert scientific minds during the World War. Owing to the complexity of the conditions, many of its problems are as yet unsolved. As modern aeroplanes po e extreme speed and power of manoeuvre, they can avoid shells by a slight change of direction— (e.g.), if a shell requires 30 seconds to get from gun to target, aeroplane flying at 120 m. has to travel a mile to meet it; by turning completely on its track it can avoid the shell by nearly 2m. This ‘dodging’ or ‘jinking’ of the aeroplane is the dominating factor in the problem, and explains the relatively small lo es inflicted on aircraft by gun-fire from the ground (est. at 7 per cent. of the whole). Role of anti-aircraft gunnery is, however, a preventive one: it forces aircraft to fly high and interferes greatly with bombing, reconnai ance, photography, and artillery observation. Anti-aircraft guns, capable of attacking the enemy suddenly and unexpectedly at ranges ‘of 8,000 or 9,000 yds., provide the moral deterrent to all these forms of activity. Surprise is the e ential of succe both for aircraft and gun. The aeroplane appears often not more than a minute, carries out its busine , and is gone; in the first half-minute the gunner has to make all his measurements of height, speed, and direction, determine the right fuse-setting, set the fuses, load, aim, and discharge his gun. Complicated calculations are, therefore, out of the question, and the instruments employed must be as simple and automatic as po ible. The problem is all the more difficult because the range-error is often impo ible to determine and, always usele when determined, because it refers to the past. Much ingenuity has been expended in devising means of predicting the future position of the target by the use of instruments measuring the elements of its present position (speed and course). During the war long-base range finders (500 to 3,000 yds. apart), working with telephonic or electrical communication, were generally used, but were inferior to the most recently designed mono static optical instrument. The range being obtained. it was nece ary to determine either the course and speed, or the angular velocities of the target about two axes at right angles, in order to predict the point at which to aim the gun. | This required complicated instruments and highly trained observers. Fuse-setting was determined graphically by a ‘height fuse indicator,’ employing the height, angle of sight, and vertical deflection as data. Finally, if the highest accuracy was required, corrections had to be superimposed for effect of wind on shell, effect of density of air, wear of gun, and temperature of charge, on the trajectory, ‘drift’ to the right caused by the rotation of the shell and abnormal burning of the fuse. In practice the proce es were carried out in rather a rudimentary fashion, owing to the extremely important tactical advantage of engaging the enemy without delay. Guns mostly employed in anti-aircraft work were of about 3-in. calibre, firing 12% or 16 lb. shells. The French 75 mm. _‘auto-cannon’ was most effective. Brit. worked largely with improvised mountings till the end of the war, the chief gun (‘archie’) employed being the 13-pr. 3 cwt.) mounted on a lorry. The 3-in. 20 cwt.) gun, specially designed for anti-aircraft work, was also largely employed, but gave much trouble with fuses and shells and was not as mobile as the 13-pr. One of the main difficulties of anti-aircraft work was the bad behavior of fuses, a variety of conditions (mow well understood), causing large errors and many ‘blinds.’ Investigation of these and other problems—(e.g.), effect of wind and atmospheric density, the dynamics of shell flight, laws of resistance of the air—has had a remarkable scientific reaction on development of ordinary gunnery,