Mr Stewart is the editor of the British publication Aeronautics. He also serves as commentator on aviation matters for the British Broadcasting Company and as aviation writer for the London Observer. A pilot in the first World War. he was awarded the Air Force Cross for his part in early experimental dive bombing. Born in 1895. he joined the Middlesex Regiment in 1914 and transferred to the RFC in 1915. He was credited with downing seven enemy planes and was awarded the Military Cross.
Attention has focused mainly on long-range strategical bombing. The great raids on Cologne and other German cities were the first cause of this and since then the statement by Air Marshal Sir Arthur Harris has intensified interest. There has been as a result a great deal of talk about the possibility of knocking Germany out by long-range bombing.
It can be predicted with a certain amount of assurance, however, that attention will eventually swing back to close support bombing, and it is about this that there is the greatest difference of opinion in Great Britain at the present time. Close support bombing may be defined as bombing designed to prepare the way for the advance of land forces. It has its counterpart in naval warfare, but for the moment I confine myself to discussing the land aspect and especially the aspect concerned with dive bombing.
There has been more vigorous dispute about the value of dive bombing than about almost any other tactical operation. The Royal Air Force has not, during the present war, been in favor of dive bombing. In 1939, the Air Staff was definitely against it. Yet before that the Royal Air Force had done a great deal of development work mainly with Hawker Hart aircraft on dive bombing both for land and for sea targets, and when war started in September, 1939, some of the Fairey Battle squadrons that went to France as part of the Advanced Air Striking Force were practiced in the technique of dive bombing.
But even so, the official air force view was opposed to it. It remained opposed to it during the German successes in France and elsewhere. It refused to be deflected by the successes achieved by the German dive bombers. It argued always that the dive bomber is highly vulnerable to fighter aircraft and that it is in itself a type whose duties can be better performed by other machines.
In spite of the Royal Air Force view, however, the Ministry of Aircraft Production, believing that the need for dive bombers existed and being supported in his by army views, ordered from the United States a number of dive bombers in July, 1940. This was during the period that Lord Beaverbrook held the position of minister. Even after this order had been placed, however, the Air Staff's anti-dive bomber views found repeated expression not only in official documents but also in such unofficial newspapers and other publications as were ready to present the official view.
My own opinion is and always has been that dive bombing will become obsolete just as soon as but no sooner than the bomb. In other words, I believe that the Air Staff was mistaken in rejecting the dive bomber as a means of giving close support to land forces and also as a means of cooperating with sea forces. It is worth here putting the two sides because of the extreme importance that American opinion should have the arguments before it and should make its own decision as to which argument is right.
In 1918, I was engaged on experimental flying for the Royal Air Force and I did a certain amount of work in the early development of dive bombing. The theory has remained exactly the same today as it was then and it may be stated thus:
Now take these points separately and contrast them with the case of the level bomber. In the level bomber the bombardier sights in a direction totally different from that taken by the aircraft. He sights at a steep downward angle while the aircraft is flying horizontally. Therefore points (1) and (2) show a sharp difference between the two methods of launching a bomb. The level bomber bombardier sights in one direction while the bomb leaves the aircraft traveling in a totally different direction. It must thereafter curve over and down as it moves towards the target. In brief, the bomb launched from the level bomber goes round a corner towards its target whereas the bomb launched from the dive bomber goes almost straight.
Now take the third point. The level bomber throws its bomb in a horizontal direction and if it is flying at 300 mph it gives it an initial impulse of 300 mph horizontally. The bomb gathers speed as it curves over and down and the extra speed it will acquire depends on the height of the launching. But the fact that the initial impulse is in the "wrong" direction is a cause of inaccuracy. If the extreme case is taken of a dive bomber diving absolutely vertical in still air the bombardier would not need to aim off from his target on the ground or to make any calculations whatever. He would simply aim and sight straight down. The dive bomber does not normally attain a vertical dive (though the theory that it cannot do so is by no means proved). But the closer the aircraft is to the vertical the more nearly is the bomb sent off in the direction of the target and therefore the greater the accuracy.
Dive bombing was devised as a method of close-range bombing. Close range gives accuracy for many obvious reasons. The level bomber can launch its bomb at close range. If, for example, the dive bomber releases its load at 1,500 feet the level bomber could do the same. But the flight of the two bombs would be totally different and the bomb from the level bomber would be inclined to "bounce" if it were of the delayed action type. If it were not of the delayed action type it would probably throw up fragments which would damage the aircraft. This bouncing is a very real trouble in low-level bombing. But it does not happen with the dive bomber because the bomb is flung directly at the target and does not strike it at a flat angle.
The fifth and final point is that the bomb is given additional impulse in the direction of the target. When the target is a very well protected one, it is of value if the bomb can be given as high a speed as possible, because the penetrative powers of the bomb go up with the speed. There are two ways of giving the bomb speed: by launching it from an enormous height or by launching it in the dive. If the bomb can be launched from 30,000 feet it will acquire a greater speed than it can be given by a dive bomber working at 2,000 or 3,000 feet, but the height means that the target cannot be clearly seen and that many aiming errors come into the picture. Therefore dive bombing should always be compared with low-level bombing. In this case it has an advantage in penetration. If the dive-bombing aircraft is dived at 250 mph, which is the approximate rate the German dive bombers attain with air brakes in full operation, then the bomb is given an additional impulse in the direction of the target of 250 mph and this is in the proportion of at least one-third the speed the bomb would gain if dropped from a great height. It is therefore a useful addition to the bomb's speed. More modern dive bombers than the Germans use, with really sound air brakes, should be capable of making their dives at higher speeds while retaining full control and the ability to flatten out without difficulty, but probably dive-bombing speeds would not go much above 300 mph.
These are the points about dive bombing which have not been widely understood in Great Britain. Many people in official positions have not understood them and that is why there has been in Parliament and outside it a good deal of muddled thinking about the dive bomber. It is perfectly true that the dive bomber is highly vulnerable to fighters but so are all low-level bombing aircraft. Fighters must clear a way for any kind of close support bombing and if they succeed in clearing a way the dive bomber is as secure as other types.
At the time that these notes are being prepared United States dive bombers are coming into service in the Royal Air Force, though they have still not been reported in action. But there have been rumors that they will be converted to other uses. If I may express a personal opinion I would say that any such conversion would be a mistake. These aircraft were originally designed for dive bombing. They have air brakes of approved pattern and they could be extremely useful as dive bombers.
After dive bombers the subject that has probably been most in the minds of those concerned in British service aviation is that of the new fighters. The Focke-Wulf Fw-190 has for some time been in the hands of the technical department of the Air Ministry and has been thoroughly examined and its performance noted. It is regarded by Air Force pilots as an extremely good machine. Its performance is excellent with the top speed of 375 mph at 18,000 feet and a rate of climb at height of well over 3,000 feet per minute. The BMW-801 engine in particular has attracted widespread praise mainly on account of the fan cooling and the sliding ring in the nose which enables air flow around the cylinders to be adjusted. This engine will repay close study by engine makers. It is obviously a fine piece of work.
The aircraft itself is an all-electric machine with a high degree of automaticity. Undercarriage retraction, the working of the wing flaps, the engine controls and other items are interlinked in an ingenious manner so as to reduce the separate functions necessary to be done by the pilot.
The aircraft's armament of four 20-mm cannon and two machine guns is not particularly advanced, except that it is the first time that cannon have been synchronized to fire through the disc swept by the airscrew blades.
It has been known for some time and the fact was confirmed by Colonel Llewellin, Minister of Aircraft Production, that a new machine is coming forward which is superior to the new types of the enemy and there is a reasoned confidence that these new machines will give Royal Air Force fighter pilots another slight technical lead over the enemy.
One of the new types is the Hawker Typhoon with Napier Sabre engine. It as been expected in service for more than a year and the delay has caused some slight disappointment here and there. But most people who are familiar with the problems of putting a new aircraft into service were less inclined to believe that this machine would go through all the development stages with the rapidity that was at first expected. They ere not therefore so disappointed when delays occurred and this is especially so in that the Napier Sabre engine is a revolutionary type of power unit showing a greater compactness for its power than any other existing aero engine. It is, as readers of Flying will know, a 24-cylinder H-type engine with two crankshafts geared together at the main shaft. It was designed by Maj F B Halford.
It is a "box of tricks" with everything packed in so closely that there is no free space left. But if it can be made to work well this engine might easily prove to be the outstanding technical feat of the entire air war, for its possibilities of development are very great and the announced horsepower of 2,000 is obviously a conservative preliminary figure which we may expect to see greatly stepped up in the future. The Typhoon therefore may prove a good competitor for the Focke-Wulf Fw-190.
So once again we have the position that the time factor is the deciding one. It will be a question of whether the enemy manage to get the Fw-190 into service in greater numbers than our newer machines when the next big flare-up in the air war occurs. Some Spitfires now carry increased armament, in the shape of four cannon.
Everybody in the Royal Air Force is interested to see how the Republic Thunderbolt will behave, for in this machine it is possible that the Focke-Wulf may meet its master. However, there is very little information available in Britain about the Thunderbolt and only very general figures have been published here.
During the cloudy days of July and August the Royal Air Force made a large number of daylight raids on Germany itself. Nearly all these raids were made with the aid of cloud cover, for it is not considered practical to send bombers for great distances over enemy-held country in the daylight without such cover. Only in very special cases such as the Augsburg raid by Avro Lancasters and the raid on Danzig (also by Lancasters) is it thought worthwhile to take the risks of heavy losses which are entailed in daylight bombing operations.
But by utilizing cloud cover the Royal Air Force Bomber Command has been able to send over aircraft such as the Vickers-Armstrongs Wellington and to find targets in Germany and bomb them without great risk of loss. The Germans have done the same kind of thing against England and have sent bombers over in the daylight using cloud cover, but they have not done it to quite such a large extent as the Royal Air Force. These raids are merely intended to maintain the pressure of the night raids. They are never made on a large scale for the mere fact of the use of cloud cover precludes this.
But the whole question of the use of daylight raiding is resurrected by these raids. It is still held here as it always has been that for precision bombing the daylight is necessary. At night the use of dummy fires and of decoy camouflage is now so ingenious that the most skilful pilots are apt to be misled and to waste their bombs. Only the mass bombing of the kind employed by Air Marshal Harris can be entirely effective for night work. For the hitting of a precise target such as a particular factory or some specified harbor equipment the daylight must be used and the question has exercised many minds of when and how the Royal Air Force will be able to bomb Germany in the daylight, in force and without the use of cloud cover. Here again opinions are divided but there is a fairly general agreement that only two methods are possible. One is to use high-flying machines, and the other is the use of fast-flying machines. If medium bombers can produced capable of speeds of 350 mph they would stand a good chance of raiding Germany in daylight without suffering heavy losses.
It is instructive to notice that the Douglas Boston bombers which are among the fastest bombing aircraft in the Royal Air Force have suffered very small casualties during their raids on occupied France. It is true these raids are comparatively short-range affairs, but they are done in broad daylight sometime without fighter cover and they do testify to the value of high speed. As for high altitude work this depends upon the turbosupercharger, a thing which the United States have developed further than most other peoples. But the turbosupercharger is not the only need for high flying, as we all know now numerous other factors have to be considered and the problem of keeping the crew alive and efficient at great heights is still not entirely solved. But in the eventual crushing of Germany it is generally believed that the night bombing must no only be intensified so that raids on the scale of the thousand-plus Cologne raid of the 31st of May are frequent, but also that they must be supplemented by daylight raids by strong medium and heavy forces.
This article was originally published in the November, 1942, issue of Flying including Industrial Aviation magazine, vol 32, no 5, pp 28-29, 92, 94.
The original article includes a thumbnail portrait of the author and 3 photos: