Saturday, 28 January 2017
Pz.Kpfw.III Ausf. A: Christie, German Style
The appearance of John Walter Christie's Medium Tank M1931 caused a revolution in tank building worldwide. A new type of tank appeared: the fast tank. Thanks to their speed, these tanks could carry out a number of other tasks in addition to infantry support. Many countries began working on conceptually similar tanks. The PzIII, Germany's main tank in 1940-43 could be considered one of these tanks. What is the history of its creation?
A New Class
In the early 1930s, German engineers worked on two types of tanks in utmost secrecy. One of them, the Grosstraktor (large tractor) was a 16 ton medium tank. The second, the Leichttraktor (light tractor), was a 9 ton tank armed with a 37 mm gun. Similar in concept to the American Light Tank T1, inspiration was also drawn from the British Medium Tank Mk.I. The main purpose of the light German tank was infantry support. The work was done in a tender: one tank was built by Rheinmetall and one by Krupp. The tanks were tested in the USSR at Kazan. After the trials, changes were made to their suspension.
Meanwhile, the late 1920s and early 1930s were a time of change for worldwide tank building. Despite a financial crisis, several iconic vehicles were made. The duet of John Carden and Vivian Loyd joined forces with the arms giant Vickers-Armstrongs Limited, birthing the Carden-Loyd tankette and Vickers Mk.E light tank. Even though the British army skipped over both tanks, they had an enormous influence on tank designs in other countries.
Germany was no exception. In 1931, it purchased a Vickers-Carden-Loyd artillery tractor, which had the same layout as their tanks. Trials showed that a layout with a front transmission has its advantages. Taking the British vehicle as the base, the Germans developed a new tank called the Kleintraktor. It not only became the foundation for the PzI infantry support tank, but defined the concept of the German tank as a whole. According to this concept, the German tank had a gasoline engine positioned in the rear, with a transmission and drive sprockets in the front. The turret was installed on a removable turret platform.
One of Rheinmetall's Leichttraktors received a suspension with coil springs in 1933. This was the first step towards the future PzIII.
The appearance of the Christie tank put the Leichttraktor into an even shakier position. Experiments with it continued until 1933, but it was clear that the time of the "light tractor" is done. Germany took a serious interest in the American tank. According to Peter Chamberlain's information, they tried to get Christie to work for them, offering a sum of one million dollars. The head of the US. Wheel Track Layer Corporation showed them the door. However, this didn't stop Rheinmetall-Borsig AG engineers from making their own version of the Christie suspension. It was tried on one L.Tr. Rhm., but did not move past the experimental stage, at least on this type of tank.
A discussion regarding the Leichttraktor's replacement began in late 1933. According to the first drafts, the 37 mm gun used on the L.Tr. was satisfactory. Full requirements for the new tank appeared later, in January of 1934. On January 27th, the 6th Armament Directorate, responsible for development of armoured vehicles, began the development of a tank armed with a 37 mm gun and weighing about 10 tons. The design was developed in close cooperation with Krupp. The arms giant couldn't wait to get even with Daimler-Benz, who took the contract for La.S. (the future PzI) right out from under their nose. Krupp expected to have their revenge by taking the contract for the new tank.
However, everything did not go according to Krupp's plan. The 6th Armament Directorate considered a competition to be a much better way. In the spring of 1934, an order for the development of a new tank was sent out to four companies: Daimler-Benz, Krupp, MAN, and Rheinmetall-Borsig. The tank was indexed Z.W. (Zugfuhrerwagen), or "platoon commander's vehicle). The index Gefechtskampfwagen 3.7 cm (combat vehicle with 37 mm gun) was also used. Finally, the experimental tank was called Vskfz 619, or "experimental vehicle 619". According to specifications, the 10 ton weight class tank would have a 300 hp Maybach HL 100 TR 10 L engine and a ZF SSG 75 six-speed gearbox. The width of the track links was also set to 326 mm.
This is how Krupp's Z.W. looked like. Only the turret went into production, as the 6th Armament Directorate didn't agree with Krupp's proposal to make the whole tank.
The proposed designs were similar in many ways. Jentz and Doyle only provide the specifications for the Daimler-Benz, MAN, and Rheinmetall-Borsig designs. However, Krupp also finished their design, and even completed a full sized wooden model. According to existing information, the mass of all proposals was about 12 tons, the length was between 5.1 and 5.4 meters, the width was about 2.6 meters, and the height was about 2.4 meters. Sadly, no graphical materials of original designs remain.
Based on examination of the projects, the work on the chassis and the turret was split up. DB and MAN received a contract to build one chassis each, and Krupp and Rheinmetall-Borsig received a contract to build turrets. Krupp's engineers continued work on the chassis, but they couldn't pull off another B.W. style gambit. That design did not progress further than a wooden model. Soon, MAN left the competition, and DB received a contract for two experimental chassis. At the end of 1934, the tank received the name 3.7 cm Geschütz-Kampfwagen, or fighting machine with 37 mm gun.
On the Way to Production
Experimental prototypes of the Z.W. were completed in August of 1935. By then, the tank was renamed again, into 3.7 cm Geschütz-Panzerwagen, or "armoured vehicle with 37 mm gun". Work on turrets continued, with Krupp finishing not one, but two prototypes.
The dimensions of the Daimler-Benz chassis was slightly different from the initial characteristics of the Z.W. It was 40 cm longer and almost 20 cm wider. As specifications required, it used a 300 hp Maybach HL 100 TR engine and ZF SSG 75 gearbox. Even though the top speed was estimated to be 40 kph, one must not forget about the Christie tank. At the same 12 tons, it had a 343 hp engine. The weight and engine power characteristics are close enough to make one doubt that it was a coincidence.
Rheinmetall-Borsig turret design.
The suspension was another indicator of what the Germans were inspired by when making the tank. As mentioned above, the German take on the Christie suspension was tried out on the Leichttraktor. This suspension migrated to this tank without changing much. The Germans approached the spring suspension in their own way. Unsatisfied with the space the springs took up inside the tank, the Germans put them outside. The length of the spring was also a lot less than on Christie's tanks. The road wheels, five per side, were also smaller. The suspension used on the American Gun Motor Carriage T49 was similar, and that was likely also no coincidence.
The same turret installed on an experimental Z.W., 1935.
The similarities ended there. The drive sprockets and idlers were completely different, and the layout of the tank had little in common with the "American". The Germans used large diameter idlers and a drive sprocket with teeth rather than bars. The crown was removable. The drive sprockets and transmission were located in the front of the hull, which allowed the size of the fighting compartment to be increased. The track links were a departure from the original requirements and their width was increased to 360 mm.
The hull also had little in common with the American tank. It turned out rather wide. The driving compartment fit not only the driver, but a radio operator/hull gunner. Thanks to the "step" shape of the front of the turret platform and observation devices that pointed sideways, the driver had good visibility. The thickness of the armour ranged from 10 to 14.5 mm and protected from rifle bullets. Experimental Z.W. tanks were made of mild steel.
The second Z.W. was built with a Krupp turret.
Alternative turrets were ready by August of 1935. Both of them were designed to house three people, with the commander sitting in the back and looking through a commander's cupola. Influence from the Nb.Fz. medium tank and La.S. turret could be seen here. The Nb.Fz. shone through the hardest in the Rheinmetall turret. The commander's cupola was taken with no changes, and the hatches on the sides also looked very similar, and also opened backwards. The shape of the turret looked like a larger version of the one developed for the La.S. by Daimler-Benz. The sides and rear of the turret were made from one curved plate, which was not great when it came to ease of production. The gun had an external mantlet.
This turret went on to initial production PzIIIs.
Krupp engineers also based their design on the Nb.Fz. Like Rheinmetall, the commander's cupola and hatches took their influence from there. Krupp was also designing the turret for the B.W. support tank, the future PzIV, and the turrets of these tanks had many similarities. After trials that took up the rest of 1935, it was clear that Krupp's design was superior. A list of 25 improvements was made, but this did not seriously dampen their success.
In April of 1936, the tank finally obtained the index it is known by today. It became Panzerkampfwagen III (3.7 cm), or "armoured fighting vehicle III with a 37 mm gun". At the same time, it was given the index Sd.Kfz.141, or "special purpose vehicle 141". A year later, a batch of 10 tanks was completed, with serial numbers 60101 through 60110.
Mass production PzIII Ausf. A from the 5th Tank Regiment, 3rd Tank Division.
While the layout and shape of the turret and hull remained the same, the first PzIII Ausf. A tanks had a number of differences from the initial Z.W. First of all, this applies to the suspension. The drive sprockets and idlers became smaller in diameter. The design of the suspension, which now had shock absorbers for the road wheels, was also different. The tank received observation hatches, and the driver had a special observation device for battle. The Mayback 100 TR was replaced by the HL 108 TR with a volume of 10.8 Liters and power of 250 hp.
The same tank on exercises.
The turret also underwent changes. The first variant of the gun mantlet was deemed unsatisfactory and had to be changed. The design of the commander's cupola was also changed. The use of the tank revealed that machinegun fire often damaged the antenna. A deflector rail was installed underneath the gun mantlet to move it out of the way.
The changes made to the suspension can be seen here.
The small size of the first batch (10 tanks) can be explained by problems with the suspension. The Germans ran into the same problem as the Soviets did with later versions of the BT tank and then the T-34. The problem is that Christie's suspension was sensitive to increases in mass. The mass of the PzIII Ausf. A was 15 tons, 3 tons (25%) heavier than the Z.W. The result of the increased load was an increase in the oscillations of the hull, and the addition of the shock absorbers didn't help much. These problems were likely discovered during trials, as Daimler-Benz received a contract for Z.W.3 and Z.W.4 tanks with leaf spring suspensions back in 1936.
Tank from the 1st Tank Regiment, 1st Tank Division during fighting in Poland. September 1939.
Despite issues with the suspension, the PzIII Ausf. A not only reached the front lines, but saw action. The reason for this was simple: there were no other medium tanks. Ironically, there were more heavier PzIV "support tanks" produced than PzIIIs. Production of the PzIII only surpassed 10 units per month in July of 1939.
The first mass produced PzIII tanks were put into the 1st Tank Regiment, 1st Tank Division and the 5th Tank Regiment, 3rd Tank Division. These tanks were actively used in exercises and frequently appeared in photographs. Initially, they were painted in three colour camouflage, but were repainted in the 1938 dark gray colour by the start of WWII. The tanks saw combat in 1939 in the same units. They were only taken off the front lines when enough PzIII Ausf E-G tanks were delivered to tank units.
PzIII Ausf. A from a training unit. The tank carries its original 3 colour camouflage.
The tank's service did not end here. These tanks were transferred to training units and spread out among many training facilities. Some tanks had their turrets and turret platforms removed and drove around like this for a few more years. The PzIIIs Ausf. A were finally written off only as they wore out.
Converted tank. It has a new machinegun mount and a Notek light. Smoke grenade launchers would have been installed in the rear.
Despite its difficult beginning, it's hard to call the Z.W. a failure. Yes, its suspension was poor, and caused a few years of headaches. However, overall, especially as the first German medium tank, the design wasn't bad. It had a sizeable modernization reserve built in. Final production PzIII tanks were 1.5 times heavier than the PzIII Ausf. A, and their front armour was three times as thick.
By 1939 the tank was the best medium tank in the world, and only the appearance of the T-34 spoiled this situation for the Germans. It's worth mentioning that the PzIII was superior to the T-34 in some areas, especially visibility. However, the story of the transformation of the Z.W. from an ugly duckling to one of the best tanks in the world by the start of WWII is worthy of another article.