While the taper and squeeze bore experiments were progressing, another system of improving performance began to attract attention. The French ordnance engineer Brandt had been experimenting for some years with discarding sabot projectiles, a system in which the gun fired a projectile of less than its own calibre-a 10.5cm gun, for example, might well fire an 8.8cm projectile. In order to make the smaller shot fit the larger bore it was first fitted into a sabot (a French term for `shoe’ or `tub’) of full calibre, so engineered that upon leaving the muzzle the sabot was discarded and fell clear to leave the sub-calibre projectile free to proceed to the target. The advantages of this system were manifold; the gun did not require any special adaptors or methods of construction (although subsequent experience has shown that the twist of rifling can be fairly critical), the composite projectile and sabot was lighter than a standard projectile for the gun and thus accelerated faster in the bore to develop a high muzzle velocity, and the full-calibre base area enabled the charge to develop its full potential. Yet the sub-projectile in flight had a favourable sectional density and thus retained its velocity, giving longer ranges, higher terminal velocities and consistent accuracy. As with almost all ordnance ideas, the discarding sabot was far from new; it had been patented as far back as 1862 (British Patent 2064 of 19th July 1862. granted to W. E. Newton as agent for A. A. Emery) but, as with Puff’s taper bore, the idea was well in advance of contemporary ballistic knowledge and engineering technique-and had lain unused for a long time.
When the German Army occupied France in 1940 many of Brandt’s experimental projectiles were discovered: these and the idea were taken back to Germany for development, which was done to good effect. Krupp were particularly interested and active in this field, and a wide variety of discarding sabot projectiles were produced on an experimental basis together with small numbers that were issued to service more or less in the nature of user trials.
Another weapon discovered in France, and which was considered to hold promise, was the Bassett gun. The brainchild of a French engineer of the same name it was a hyper-velocity 3.7cm gun whose principal feature was the burning of propellant at hitherto unconsidered pressures. Instead of the usual order of 20 to 25ton/in2, Bassett proposed operating his gun at 95 to 100ton/in2. Since normal rifling and driving bands could not hope to cope at such levels, the barrel was shaped internally into a twisted octagon that, as it approached the muzzle, blended into polygonal (perhaps 16- or 32-sided) shape. The shot was provided with multiple sealing bands of soft iron and Buna rubber, and was of octagonal section to match the barrel; thus it attained spin, a reversion to the Whitworth system of rifling which was briefly touted in the 1850s and 1860s. In order to utilise the expansion of the propellant gas, and thus develop the utmost efficiency, the barrel was 175 calibres long (21ft 3in/6.48m). Bassett signed a development contract with the German Army but progress was slow, since much basic research had to be done before manufacture of the weapon could begin; nobody, for example, was quite sure what would happen to a conventional smokeless propelling powder when it was burned at such high pressures, and special pressure chambers had to be designed in which samples could be ignited and their performance studied. All this took time; and in 1944, before the work was completed, the Allied armies invaded France. When Paris was abandoned by the Germans Bassett moved to Switzerland, but the gun and experimental apparatus were removed to Germany in order to continue development. It soon became apparent that the weapon would never become a viable mechanism in time to influence the war’s course and work on it stopped entirely early in 1945. While undoubtedly an interesting concept in ballistics and physics, there seems little useful purpose in the weapon and it has never been revived.
The next project to be examined in the search for longer range was the possibility of providing in-flight assistance to the projectile by means of a rocket boost. The idea was again as old as ammunition, one typical proposition being Taylor’s British Patent 1460 of 20th May 1870. Considerable work had already been done in Germany on rocket propulsion and, on the face of it, a rocket-assisted shell sounded most attractive. Numerous designs were tried and two or three were actually issued for service, but the drawbacks were well-nigh insuperable. The rocket propulsion firstly demanded an excessive amount of the limited space available in the shell, leading to a small explosive payload which was hardly worth the expense and effort of getting it to the target. Secondly, the gun shell was rarely-if at all-perfectly aligned with its theoretical trajectory; it was invariably `yawing’ about the perfect line in one direction or another. At the instant the rocket motor ignited and began to deliver thrust, any off-line yaw of the shell resulted in the rocket trajectory being a continuation of the yaw axis and not necessarily the axis of the ballistic trajectory. As a result, the projectile could land anywhere in a large probability area around the intended target. This, coupled with the small payload, rendered the long-range rocket shell an uneconomic proposition, though it undoubtedly had its advantages as a propaganda weapon.
A further disadvantage of the rocket-assisted shell, as seen by some scientists, was the necessity to carry both the fuel and an oxidant required to promote burning. Had it been possible to carry only the fuel and tap the ambient air as the oxidant, then the propulsion unit could have been made smaller by the amount saved in oxidant storage space and the explosive payload correspondingly increased. Dr Tromsdorf spent much time and effort developing his `pulsating athodyd’ shell, which was really a ram-jet running along the axis of a projectile. A quantity of liquid fuel (usually carbon disulphide) was carried and as the incoming air mixed with the fuel in a combustion chamber it was ignited, and the resultant thrust boosted the shell. This development was being explored with a view to improving anti-aircraft gun performance, but the work was still in the experimental stage when the war ended. It is believed that both the Americans and the Soviets showed some interest in the idea during the immediate postwar years, but the inaccuracy problem still existed and the promised increase in payload was largely illusory owing to the space needed for the induction, combustion and exhaust systems. The athodyd shell, while theoretically sound enough, is no longer considered to be a practical proposition. The last field of endeavour, and one which held considerable promise, was the development of fin-stabilised projectiles. Gun shells are customarily spun by the rifling to achieve gyroscopic stability but this system has some inherent limitations. As has already been seen, high velocity guns made considerable demands on the system of rifling and banding, owing to the high rotational stresses thus developed. Furthermore, the pressures needed to engrave a driving band were on occasion quite large and led to undesirable peak pressures in the gun chamber. The projectile was restricted in length, since shells much more than six calibres long could not be satisfactorily stabilised except at very high spin rates, which in turn demanded special rifling and multiplebanding to spread the load on the shell and driving bands. The fin-stabilisation solution promised freedom from most of these troubles and in some cases offered a simpler gun into the bargain, since the weapon could thereafter be a smooth-bore. The reasons for adopting fin-stabilisation varied from attempts to obtain high velocity-by removing the frictional resistance of rifling and banding-to stabilising projectiles too long for conventionally rifled guns, in the case of some special designs of anticoncrete shell. Fin-stabilised projectiles could also be fired from a rifled gun and yet avoid much rotation, in order to improve their tactical effect.
Much of the theoretical development in this field took place at the Raketen-Versuchsstation Peenemünde (Peenemunde rocket research establishment) where wind tunnels were available and where there was considerable knowledge of the aerodynamics of finned missiles. The principal outcome of their work was the Peenemunder Pfeilgeschoss (Peenemunde arrow shell) which was developed both as a long range terrestrial-fire projectile and as a high velocity projectile for anti-aircraft work. Little of this work bore fruit in time to be used during the war, but it formed a considerable base for postwar development by many other nations.
All these developments illustrate the point that the easiest way to improve a gun is to leave it alone and work on the ammunition. As far as the guns themselves were concerned, development was usually aimed at improving efficiency and producing weapons that were lighter to manoeuvre; guns with greater flexibility in terms of elevation and traverse, those which were simpler to operate and those easier to mass-produce were all demanded of the designers. When producing a design incorporating as many of these desirable characteristics as possible, attempts were made to increase the range (if it could be done) but in many gases the improvement in performance was less apparent than the improvement in other criteria. In certain fields-anti-tank guns, for example-performance was so vital that the guns inevitably grew bigger and bigger: questions of handiness in action and ease of manufacture were subordinated to the overriding demand that a specific target had to be engaged and destroyed at a specific range until, towards the end of the war, it was obvious that a halt had to be called before the guns became too large for their tactical role. Fresh ballistic solutions had to be devised instead.
There had already been a demand for lightweight weapons for a special application and this had been answered by the development of recoillessguns for use by airborne troops. A number of lightweight shoulder-fired weapons had also appeared during the war, capable by virtue of the ammunition they fired of defeating most of the contemporary tanks. These weapons were the rocket launchers such as the American Bazooka and the German Ofenrohr, (`stovepipe’), and the recoilless Panzerfaust (`armoured fist’). Using hollow charge bombs, these weapons could deliver a fatal attack on a tank without need of heavy or high-velocity ordnance, and so the army then asked the manufacturers to contemplate producing some sort of gun that could deliver a hollow charge shell with accuracy, which would be light to move and easy to use, but which (in view of the economic position) would use less propellant than the rocket or the recoilless guns in the process. The response to this demand was Rheinmetall-Borsig’s development of the Hoch-Niederdruck-System (`high-low pressure system’), one of the few completely new ballistic developments to come out of the war. The high-low pressure gun confined the cartridge in a robust breech in which the explosion of the charge reached a relatively high pressure of about 8ton/in2. Between the charge and the projectile was a heavy steel plate pierced with a number of carefully designed holes through which the high pressure was bled into the lightweight barrel. In the barrel the pressure dropped to 2-3ton/in2 and it was this that moved the fin-stabilised projectile up the smooth-bore barrel, the pressure dropping to as little as 1ton /in2 at the muzzle. The system was highly successful and at least one weapon embodying it entered service; a number of others were planned but the end of the war stopped their development. In postwar years the high-low pressure system was the focus of considerable interest from ballisticians throughout the world but it has, surprisingly, seen little application since 1945.
This brief introduction serves to show that the subject of German artillery during World War 2 is one that is full of interest. Confronted as the war continued with heavier tanks, faster aircraft and more fluid warfare, the German designers were never for long at a loss for the next idea. Admittedly they sometimes produced a disaster, but more often they produced a winner and it is noteworthy that the designs that were being taken from the drawing board and into service in 1945 were examples of gunmaking which have rarely been bettered; many postwar designs owe some of their better features to ideas pioneered by Germany during the war years.