Soon after the intensified murder raids on London began the increased fury of the A.A. gun barrage gave much satisfaction to the millions compelled to endure the indiscriminate Nazi bombings. Other defence methods were also operative, and here an acknowledged authority discusses the problems of night defence and forecasts increasing success in grappling with them. One feature of the air war which showed a steadily increasing importance from the beginning until the time of the intensified aerial attacks on Great Britain of August and September was night bombing. And in countering it the greatest ingenuity was exercised. Night bombing was begun by the Royal Air Force, which had carefully prepared for it and trained for it. The German air force, in so far as official statements from Berlin revealed its beliefs, held that military effect, which is the only, kind of effect worth thinking about in war, could be secured only by day bombing. Actually the Royal Air Force had evolved a method of night bombing which enabled it to hit at military targets by night with as great certainty as by day, the only difference being that the targets had to be chosen in relation to their position and also in relation to the weather. Nights do occur occasionally when the illumination is so good that targets can be recognized almost as readily as by day. But on most nights the targets chosen must be of the “self-illuminated” variety if they are to be found without the use of parachute flares or the starting of fires at near-by points. A good example of a self-illuminated target is a blast furnace. Another was the seaplane base at Sylt, which was one of the first land objectives attacked by the Royal Air Force during the war. Water can be distinguished from land on most nights, and when the shape of the shore or coastline is distinctive a target can be recognized by the conformations with as great accuracy as by day. The German air force had made many night raids before the main attacks on London began in August and September; but they had been directed at military objectives, and as those objectives are extremely well camouflaged and as England is a country over which it is exceedingly difficult to find the way ever by day, the German pilots in most cases missed their objectives altogether and dropped their bombs more often than not in open country. These small raids were the subject of many official communiques and in all cases the damage was slight or even altogether non-existent. But when the order was given to attack, London both by night and by day the method selected was very different. It seems, from the results, that any big building which could be seen by the German night pilots was to be regarded as a permissible target, and that, supposing the buildings could not be distinguished at all owing to the darkness, any cluster of houses was to be regarded as a permissible target. Thus the East End of London received a great many heavy attacks and vast numbers of dwelling houses there were destroyed. In addition, many big buildings in the West End were hit and much damage done to them. But there was no evidence that anything approaching a military target was selected by any pilot. Sometimes it did seem that power stations and railway stations were being selected, but then a large series of raids would intervene in which no bomb dropped near such objectives. The fact that this random or semi-random method of bombing was adopted by the Germans made the problems of defence more difficult. For it is clear that an airman is bound to find some part of London if he sets out for it even on the darkest night? To try to prevent enemy aircraft getting to any part of London or other large cities, while at the same time maintaining adequate protection for the real military targets such as d munitions works, was the essence of the defence problem. The solution, in so far as it had been arrived at by the beginning of October, was to obtain a high degree of coordination between the anti-aircraft guns, the balloon barrage and the night-flying fighters. The searchlights, which were used extensively at first, were used in a much reduced degree later for reasons which will appear. The first point which had to be taken into account was that interception by night was a matter of extreme difficulty and could only be achieved on nights of good visibility and with a certain amount of luck. The night-flying fighter, in fact, had very severe limitations. It was imperative; therefore, to build up the defence by gun and balloon barrage for night work. The guns made the first step. One night Londoners heard the night raiders met with a tremendous barrage of fire, more intense and more continuous than anything they had heard before. It was the outcome of the working of the first part of the new scheme. Instead of waiting for “seen targets” only, the gunners had been instructed to fire on sound alone and also to use certain new instruments and new methods. These included a new system of prediction. The ordinary predictor, used with the anti aircraft guns, is a calculating machine which quickly produces results from certain figures which are fed into it by the gun crews, the resultant figures giving the gun position officer the information for sighting and fusing that he wants. Now it is evident that the accuracy of the predictor’s results is of two orders; first, it makes the calculations correctly without exception and, therefore, in one part achieves 100 per cent accuracy; second, the usefulness of its results in the actual firing depends upon the accuracy of the figures which are fed into it. That is where the difficulty still lies. The height of the approaching aircraft must be correctly estimated, its speed and its course. Moreover, the predictor can only work on the assumption that speed, course and height will remain the same or will be subject to alterations which are pure guesswork on the part of the gun crew. No gun crew and certainly no predictor can tell what an enemy pilot will do with his machine during the appreciable number of seconds a shell is in the air travelling towards its target. When the, new barrage system was instituted for the defence of London by night, the limitations of the predictor were taken into account and a wider system of prediction, based on certain probabilities, was adopted, In addition, the firing of the guns was grouped according to a specific pattern so as to increase still further the probabilities of a hit. The entire system is one of probabilities. As such it was shown at once to be a great success. The searchlights were not used so extensively, so that the enemy night pilots no longer profited by their reflected light, but the sound locators came into more extensive play and enabled a barrage to be put up which did very effectively hamper the movements of enemy machines. It did not bring them down in large numbers. Indeed, this was not expected. It is known that a fairly large number of anti-aircraft rounds must be fired, the number has been estimated at between 5,000 and 6,000-in order to shoot down a single enemy machine, but the barrage effectively held off the enemy. Concurrently with the adoption of the new prediction system for the guns, there went an improvement in the effectiveness of the balloon barrage. This consisted in introducing new balloons and cables which could be flown higher, yet with the same lethal effect on any enemy machine which chanced to strike a cable. Barrage balloon height is determined by cable weight. Cable weight is partly determined by lethal effect. It is of no use to fly a balloon very high if, in order to do so, the cable must be so light that it can easily be cut by a fast-flying aeroplane. Research into the properties of cables had been going on since the beginning of the war, and the result was the possibility of flying the balloons higher with the same protective effect. An enemy machine was brought down by a high-flying balloon early in the series of night raids on London, and in general the balloon barrage may be said to have added its effect to that of the guns in limiting the area in which the enemy machines could work with any chance of getting away safely. Guns and balloons were not the only methods being tried during the period of night raids in August, September and October in order to counter the night raiders. Enormous numbers of devices were constantly under review by scientific workers and technical experts. Some of these were confidently expected to show successful results when the preliminary work on them had been completed. No more difficult type of attack to counter exists than the night-flying bomber which is seeking, not specific military targets, but any cluster of buildings it can find. But to every form of attack there is an appropriate defence, and it was recognized throughout the Royal Air Force that this form was no exception.
