The German Army recognised the need for a more powerful form of anti-tank weapon and the design of a horse-drawn, 3.7 cm anti-tank gun (designated 3.7 cm Pak L/45) by Rheinmetall commenced in 1924 and the first guns were issued in 1928. However, by the early 1930s, it was apparent that horse-drawn artillery was obsolescent, and the gun was modified for motorized transport by substituting magnesium-alloy wheels with pneumatic tyres for the original spoked wooden wheels. Re-designated the 3.7 cm Pak 35/36, it began to replace the 3.7 Pak L/45 in 1934 and first appeared in combat in 1936 during the Spanish Civil War. It formed the basis for many other nations’ anti-tank guns during the first years of World War II. The KwK 36 L/45 was the same gun but adapted as the main armament on several tanks, most notably the early models of the Panzer III.
The Pak 36, being a small-calibre weapon, was outdated by the May 1940 Western Campaign, and crews found them inadequate against allied tanks like the British Mk.II Matilda, and the French Char B1 and Somua S35. Still, the gun was effective against the most common light tanks, such as the Renault FT-17 and saw wide service during the Battle of France and the T-26 during Operation Barbarossa. The widespread introduction of medium tanks quickly erased the gun’s effectiveness; miserable performance against the T-34 on the Eastern Front led to the Pak 36 being derisively dubbed the “Door Knocker” (Heeresanklopfgerät, literally “army door-knocking device”) for its inability to do anything other than advertise its presence to a T-34 by futilely bouncing rounds off its armor.
Not surprisingly The Pak 36 began to be replaced by the new 5 cm Pak 38 in mid 1940. The addition of tungsten-core shells (Pzgr. 40) added slightly to the armour penetration of the Pak 36. Despite its continued impotence against the T-34, it remained the standard anti-tank weapon for many units until 1942. It was discovered that Pak 36 crews could still achieve kills on T-34s, but this rare feat required tungsten-cored armour piercing ammunition and a direct shot to the rear or side armour from point-blank range.
As the Pak 36 was gradually replaced, many were removed from their carriages and added to SdKfz 251 halftracks to be used as light anti-armour support. The guns were also passed on to the forces of Germany’s allies fighting on the Eastern Front, such as the 3rd and 4th Romanian Army. This proved particularly disastrous during the Soviet encirclement (Operation Uranus) at the Battle of Stalingrad when these Romanian forces were targeted to bear the main Soviet armoured thrust. The Pak 36 also served with the armies of Finland (notably during the defence of Suomussalmi), it was also deployed in Hungary, and Slovakia.
In 1943, the introduction of the Stielgranate 41 shaped charge meant that the Pak 36 could now penetrate any armour, although the low velocity of the projectile limited its range. The Pak 36s, together with the new shaped charges, were issued to Fallschirmjäger units and other light troops. The gun’s light weight meant that it could be easily moved by hand, and this mobility made it ideal for their purpose.
The replacement for the outdated Pak 36 was the 50cm Pak 38. The longer barrel and larger projectile produced the required level of kinetic energy to pierce armour . The PaK 38 was first used by the German forces during the Second World War in April 1941. When the Germans faced Soviet tanks in 1941 during Operation Barbarossa, the PaK 38 was one of the few early guns capable of effectively penetrating the 45 mm (1.8 in) armor of the formidable T-34. Additionally, the gun was also equipped with Panzergranate 40 APCR projectiles which had a hard tungsten core, in an attempt to penetrate the armor of the heavier KV-1 tank. Although it was soon replaced by more powerful weapons, the Pak 38 remained a potent and useful weapon and remained in service with the Wehrmacht until the end of the war.
The 7.5 cm PaK 40 (7.5 cm Panzerabwehrkanone 40) was the next generation of anti-tank gun to see service. This German 7.5 centimetre high velocity anti-tank gun was developed in 1939-1941 by Rheinmetall and used extensively from 1942-1945 during the Second World War. It was the PaK 40 which formed the backbone of German anti-tank guns for the latter part of World War II. Development of the PaK 40 began in 1939 with development contracts being placed with Krupp and Rheinmetall to develop a 7.5 cm anti-tank gun. Priority of the project was initially low, but Operation Barbarossa in 1941 and the sudden appearance of heavily armoured Soviet tanks like the T-34 and KV-1, increased the priority. The first pre-production guns were delivered in November 1941.
In April 1942, Wehrmacht had 44 guns in service. It was remarkably successful weapon and by 1943 the PaK 40 formed the bulk of the German anti-tank artillery.The PaK 40 was the standard German anti-tank gun until the end of the war, and was supplied by Germany to its allies. Some captured guns were used by the Red Army. After the end of the war the PaK 40 remained in service in several European armies, including Albania, Bulgaria, Czechoslovakia, Finland, Norway, Hungary and Romania.
Around 23,500 PaK 40 were produced, and about 6,000 more were used to arm tank destroyers. The unit manufacturing cost amounted to 2200 man-hours at a cost of 12000 RM. A lighter automatic version, the heaviest of the Bordkanone series of heavy calibre aircraft ordnance as the BK 7,5 was used in the Henschel Hs129 aircraft.
The Pak 40 was effective against almost every Allied tank until the end of the war. However, the PaK 40 was much heavier than the 50 cm PaK 38, It was difficult to manhandle into position and its mobility was limited. It was difficult or impossible to move without an artillery tractor on boggy ground.
The PaK 40 debuted in Russia where it was needed to combat the newest Soviet tanks there. It was designed to fire the same low-capacity APCBC, HE and HL projectiles which had been standardized for usage in the long barreled Kampfwagenkanone KwK 40 main battle tank-mounted guns. In addition there was an APCR shot for the PaK 40, a munition which eventually became very scarce.
The main differences amongst the rounds fired by 75 mm German guns were in the length and shape of the cartridge cases for the PaK 40. The 7.5 cm KwK (tank) fixed cartridge case is twice the length of the 7.5 cm KwK 37 (short barrelled 75 mm), and the 7.5 cm PaK 40 cartridge is a third longer than the 7.5 cm KwK 40.
The longer cartridge case allowed a larger charge to be used and a higher velocity for the Armour Piercing Capped Ballistic Cap round to be achieved. The muzzle velocity was about 790 m/s (2,600 ft/s) as opposed to 750 m/s (2,500 ft/s) for the KwK 40 L/43. This velocity was available for about one year after the weapon’s introduction. Around the same time, the Panzer IVs 7.5 cm KwK 40 L/43 gun and the nearly identical Sturmkanone (StuK) 40 L/43 began to be upgraded with barrels that were 48 calibers long, or L/48, which remained the standard for them until the end of the war.
In the field, an alarming number of L/48 cartridge cases carrying the hotter charge failed to be ejected properly from the weapon’s semi-automatic breech, even on the first shot (in vehicles). Rather than re-engineer the case, German Ordnance reduced the charge loading until the problem went away. The new charge brought the muzzle velocity down to 750 m/s, or about 10 m/s higher than the original L/43 version of the weapon. Considering the average variability in large round velocities from a given gun, this is virtually negligible in effect. The first formal documentation of this decision appears on May 15, 1943 (“7.5cm Sturmkanone 40 Beschreibung”) which details a side by side comparison of the L/43 and the L/48 weapons. The synopsis provided indicates very little difference in the guns, meaning the upgrade had little if any benefit.
All further official presentations of the KwK 40 L/48 ( “Oberkommando des Heeres, Durchschlagsleistungen panzerbrechender Waffen”) indicate a muzzle velocity of 750 m/s for the gun. As for the PaK 40, the desire for commonality again appears to have prevailed since the APCBC charge was reduced to 750 m/s, even though case ejection failures apparently were never a problem in the PaK version of the gun.
For reasons which seem to be lost to history, at least some 75 mm APCBC cartridges appear to have received a charge which produced a muzzle velocity of about 770 m/s (2,500 ft/s). The first documented firing by the U.S. of a PaK 40 recorded an average muzzle velocity of 776 m/s for its nine most instrumented firings. Probably because of these results, period intelligence publications (“Handbook on German Military Forces”) gave ~770 m/s as the PaK 40 APCBC muzzle velocity, although post war pubs corrected this (Department of the Army Pamphlet No. 30-4-4, “Foreign Military Weapons and Equipment (U) Vol. 1 Artillery (U) dated August of 1955-this document was originally classified).
In addition, German sources are contradictory in that the Official Firing Table document for the 75 mm KwK 40, StuK 40, and the PaK 40 dated October, 1943 cites 770 m/s on one of the APCBC tables therein, showing some confusion. (“Schusstafel fur die 7.5cm Kampfwagenkanone 40”).
The 88 mm gun (eighty-eight) was a German anti-aircraft and anti-tank artillery gun from World War II. It was widely used by Germany throughout the war, and was one of the most recognized German weapons of the war. Development of the original models led to a wide variety of guns.
The name applies to a series of guns, the first one officially called the 8,8 cm Flak 18, the improved 8,8 cm Flak 36, and later the 8,8 cm Flak 37. Flak is a contraction of German Flugzeugabwehrkanone meaning “anti-aircraft cannon”, the original purpose of the eighty-eight. In informal German use, the guns were universally known as the Acht-acht (“eight-eight”), a contraction of Acht-komma-acht Zentimeter (“8.8 cm”). In English, “flak” became a generic term for ground anti-aircraft fire.
The versatile carriage allowed the eighty-eight to be fired in a limited anti-tank mode when still on wheels, and to be completely emplaced in only two-and-a-half minutes. Its successful use as an improvised anti-tank gun led to the development of a tank gun based upon it. These related guns served as the main armament of tanks such as the Tiger I: the 8.8 cm KwK 36, with the “KwK” abbreviation standing for KampfwagenKanone (“fighting vehicle cannon”).
In addition to these Krupp’s designs, Rheinmetall created later a more powerful anti-aircraft gun, the 8,8 cm Flak 41, produced in relatively small numbers. Krupp responded with another prototype of the long-barreled 88 mm gun, which was further developed into the anti-tank and tank destroyer 8.8 cm Pak 43 gun, and turret-mounted 8.8 cm KwK 43 heavy tank gun.
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.
The 75/55-mm tapered bore 7.5-cm Pak 41.
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.