From the days of Krupp’s first experiments with steel guns and breechloading, the German gunmakers have rarely been reluctant to try something new, and the years from 1933 to 1945 saw their vast inventive resources at their peak. Even the standard service weapons often incorporated refinements not found in the designs of other nations, and when anything extraordinary was requested the results were invariably brilliant and often awe-inspiring.
For all the inventors’ brilliance, the strategic direction of the higher command (which gave the gunmakers their specifications) was less certain of its aim: thus weapon development, which promised much, frequently got side-tracked or spent too much effort travelling in the wrong direction. It was this as much as anything, aided by a certain amount of ill-advised pursuit of better designs, that was responsible for the vast range of weapons deployed by the Wehrmacht. An example of this changeable attitude was the controversy over the standard support weapon of the division-should it have been a 7.5cm gun or a 10.5cm howitzer? During World War I the army had started with a 7.7cm gun and later augmented it with a 10.5cm howitzer, so long postwar discussions took place to try and discover which of the two was the more useful weapon. Towards the end of the 1920s the argument had been resolved in favour of the 10.5cm howitzer and this duly became the standard field support weapon-but by 1943 the argument was raging once more. This time the gun triumphed at the howitzer’s expense, leading to designs of a new model that never saw fruition owing to the end of the war. Yet, at the same time as this decision was reached, development was still proceeding on improved versions of the 10.5cm howitzer. This particular line of research can be cited as one of the superfluous efforts. The original 10.5cm howitzer was massively built, but it has since been reliably estimated that over 80% of its ammunition was fired with the various less powerful charges: a gun of half the original’s weight would still have been strong enough. An improved weapon was demanded to meet an exacting specification, but it achieved little better results and consumed 20% more propellant into the bargain.
The principal lines of development in prewar guns were much the same as those followed by any other nation-intended to provide an output of reliable and proven weapons in a rational range of guns from light antiaircraft to heavy siege types, all conventional in concept and also simple and robust. While this aim was reached in most cases, there was still sufficient design capacity to allow development of more advanced weapons to be slowly pursued; much of this effort showed results during the war, when unorthodox solutions stood a better chance of being accepted.
At the end of World War I the Versailles treaty thoroughly disrupted the German armament industry. The two principals, Friedrich Krupp AG and Rheinische Metallwaaren- und Maschinenfabrik (later Rheinmetall-Borsig AG), were limited in the designs they could produce: Krupp were restricted to weapons above 17cm calibre, and RM&M to weapons below 17cm. Moreover, only a very small number of guns of the permitted calibres were allowed to be made. In order to evade these regulations Krupp came to an arrangement with Svenska Aktiebolagst Bofors of Sweden, whereby Bofors acquired the foreign rights of Krupp guns while Krupp sent a number of designers to work in the Bofors factory and thus keep their skills alive. RM&M set up a company in Switzerland called Waffenfabrik Solothurn AG, and designs originating in the German drawing office were marketed as Solothurn weapons. Through this company too, a link with Osterreichische Waffenfabrik-Gesellschaft of Steyr was maintained.
Once the National Socialists came to power most of this subterfuge was abandoned overnight, though it was not until 1945 that the details became plain -which accounts for some amusing Allied wartime intelligence reports in which Rheinmetall-Borsig designed and built guns are described as copies of Solothurn weapons. Rheinmetall also received a boost when they became part of the Reichswerke Hermann Goring `paper corporation’, which accounts for a number of cases where their design was taken into service in preference to a Krupp model.
When the war began the German high command made a serious planning error in assuming that the war would be of short duration. With this opinion firmly fixed, they then ruled that long-term development should not begin if the result could not be brought into service within one year. This had the most serious repercussions in the electronic and radar fields, but it also stifled a good deal of development in artillery. A number of promising projects were abandoned by their developers and when, later in the war, the error was appreciated and the ban removed, it required vast efforts to make up for the time that had been lost.
Once wartime development began, however, it was usually along lines laid down by the Oberkommando der Wehrmacht (OKW-forces’ high command) in an attempt either to solve some particular problem or to produce an equipment to fill a specific need. In this respect artillery development was more tightly controlled than in other weapon fields; there appears to have been few cases of individual designers pushing pet theories, resorting to political string-pulling, and scheming to obtain raw materials and production capacity so well seen-for example-in the guided missile field in 1944-5.
At the outbreak of war the artillery equipment of the Wehrmacht was standardised on a few calibres, and the weapons were in general of sound and well-tested design. The army’s field weapons were of 10.5cm, 15cm and 21cm calibres, and the design philosophy ensured that a gun of given calibre and a howitzer of the next larger calibre were interchangeable on the same carriage, thus simplifying production, supply and maintenance. Anti-aircraft defence was built around the 2cm and 3.7cm light guns, the 8.8cm medium gun and the 10.5cm heavy gun; anti-tank weapons were the 3.7cm gun and a 7.92mm anti-tank rifle for infantry use. One or two improved designs were undergoing routine development with the intention of bringing them into service as and when the need arose.
The demands of war soon spoiled this arrangement. When it came to forecasting the future, the OKW was no more visionary than any other comparable body and the appearance of new weapons in the hands of the enemy frequently led to sudden demands on designers to develop powerful antidotes. An example of this was the sudden flurry of activity in the anti-tank field consequent upon the appearance of the virtually unstoppable Soviet T34 tank. The users’ demands on the gunmakers were always the same: improve the performance of the gun, increase its range, increase its velocity, but please do not increase its weight. How these demands were translated into reality will be seen on subsequent pages but, as a general rule, the paths open to the designers were well-defined. The only way to improve the performance of a conventional gun is by increasing the muzzle velocity, and this can be done m a variety of ways.
The first and most simple technique is to increase the size of the propelling charge or to develop a more efficient propellant, while still operating the gun at the same pressure. This, in round figures, demands a four-fold increase in propellant quantity to obtain a 60% increase in muzzle velocity, and contains several disadvantages in the shape of erosive wear, redesign of the chamber and cartridge case, and economic production of the propellant.
The second simple method is to increase the length of the barrel, thus keeping the projectile exposed to the accelerating effect of the exploding propellant for a longer time. To obtain the 60% increase in velocity would demand a 300% increase in barrel length-scarcely a practical measure.
An increase in chamber pressure combined with a moderate increase in barrel length will also increase velocity. The standard 60% increase could thus be achieved by a 50% increase in pressure coupled to a 50% increase in barrel length, but again this is scarcely a practical answer. One solution, increasingly adopted by many nations towards the end of the war, was a 50% reduction of projectile weight which increased the velocity by 40%- but the ballistic coefficient (the `carrying power’ of the projectile) was proportionately reduced. Deceleration in flight was hence more rapid, leading to less range than a full-weight projectile would have achieved at the same velocity.
Owing to these conventional design limitations, the war initiated the examination of more and more unconventional solutions. One of the first, which had been developed well before the war, was the production of high-velocity guns in which the rifling consisted of a few deep grooves into which fitted curved ribs on the outer surface of the shell, imparting positive rotation. This was developed because the conventional copper driving band was incapable of transmitting the enormous torque of high velocity projectiles’ excessive radial acceleration without shearing. The ribbed or `splined’ shell solved the problem of transmitting spin, but a copper band still had to be fitted to provide the gas-seal necessary at the rear of the shell. This was an expensive and complicated solution, suited only to large weapons produced in limited numbers, and much research was begun to try and overcome the torque defect of the copper driving band, with the additional incentive of trying to find a material in less critical supply.
The first development was the Krupp Sparführung (KpS) band-a bimetallic band of copper and soft iron, although zinc was sometimes added to dilute the copper and to assist in effecting the iron/copper joint. There was little or no performance advantage, merely an economy of copper. Next came the Weicheisen (FeW) soft iron band, the use of which was restricted to large calibre high-velocity guns. It could withstand torque very well, but the process of putting the band on the shell (by a powerful radial press) work-hardened the metal to the point where it became difficult to `engrave’-or force into the gun’s rifling. It was this defect that restricted Weicheisen bands’ use to high-pressure large-calibre weapons.
The final development was the Sintereisen (FeS) wintered iron band, formed from small iron particles bonded together under intense pressure to form a malleable band. This engraved well, resisted shear stresses, and was economical of material in short supply, but in its first application was found to wear out the gun barrels faster than a conventional copper band. Further development evolved a new form of barrel rifling with wider lands and grooves, and this-together with the reintroduction of increasing twist-improved matters to a degree where the German technicians opined that even if they had sufficient copper available they would still prefer to use sintered iron, particularly at higher velocities. One interesting result was the discovery that, while copper bands resulted in the gun barrel wearing out first at the chamber end of the rifling, FeS bands promoted wear at the muzzle since the coefficient of friction was directly proportional to the velocity.
When the increases in performance made available by increasing the barrel length and the size of the charge, and the provision of improved rifling and banding, had been taken to their extremes, it became necessary to explore less well-trodden paths. The first unorthodox solution offered was the `coned bore’ gun, the theory of which predicated that if the barrel was made with a gradually-decreasing calibre (and if the projectile was designed to adapt to the diminution) then, since the base area of the shot is reducing while the propelling gas pressure either remains-depending on the cartridge design-constant or increases then the unit pressure on the shot base will increase and the shot will be given greater velocity. The original idea was patented in 1903 by Carl Puff and the drawings accompanying the specification (British Patent 8601 of 27th August 1904) show a projectile almost identical to those later developed in Germany. Puff, however, does not appear to have pursued his ideas as far as a working gun, and the idea lay dormant until taken up by a German engineer named Gerlich in the 1920s. In co-operation with Halbe, a gunmaker, he developed a number of high-velocity sporting rifles with tapered bores and flanged projectiles, marketed in limited numbers during the 1930s under the name Halger, while at the same time attempting to interest various governments in the possible use of these weapons as high velocity military rifles. He also worked for both the United States’ government and the British Army on taper-bore rifles, but neither felt that there was much virtue in the idea; Gerlich returned to Germany c. 1935, and his subsequent activities have escaped record.
By this time others were exploring the idea: Rheinmetall-Borsig, Krupp, Bochumer Verein and Polte-Werke all had experimental programmes varying in degree of involvement. Rheinmetall-Borsig eventually became the most involved; the firm’s Dr Werner Banck, who took charge of development in late 1939, continued to work on it throughout the war and ultimately became one of the most knowledgeable men in the world on the subject of taper-bore guns.
Two classes of weapon were eventually categorised: the taper bore, in which the barrel tapered evenly from breech to muzzle, and the squeeze bore, in which the barrel was parallel for some distance and then tapered sharply to effect the `squeezing’ of the projectile, finishing as a parallel bore of smaller dimension. An alternative design of squeeze bore was one in which a tapered extension was placed on the muzzle of an otherwise conventional gun. The projectiles used with these two classes were much the same in design, though experience showed that the taper bore shot had to be somewhat stronger in construction than the squeeze bore models owing to the different times throughout which the shells underwent stress in compression.
Towards the end of the war the taper bore concept was gradually discarded in favour of the squeeze bore designs, since these were a good deal easier to manufacture. Making a tapered and rifled gun barrel was no easy task, even with sophisticated machine tools, whereas production of a smoothbore `squeeze’ extension to fit the muzzle of an otherwise standard gun was much less exacting and less wasteful of time and material. Weapons as large as 24cm calibre were fitted with such extensions (in this case reducing to 21cm) and were fired quite successfully.
The only active-service use of the taper or squeeze systems was in the anti-tank class, where three weapons (2.8cm/2.1cm, 4.2cm/2.8cm and 7.5/5.0cm) entered service. In the anti-aircraft field, while the velocity increases gave promise of considerably improved performance and where many experimental weapons were built and fired, no guns were ready for service before the war ended. There was a rule of thumb that said a squeeze bore adaptor could be expected to increase velocity and maximum range by about a third. Velocities of as much as 1400mps (4595fps) had been achieved but it was felt that, bearing in mind wear-rates and dispersion at extreme ranges, service velocities of 1150-1200mps(3775- 3935fps) might be consistently reached. The design of projectiles was an involved business and will be discussed elsewhere.