In the early 1930s, Poland built the TK-S, a very good design based on the British Carden-Loyd Mk.VI tankette. A similar thing happened with light tanks. Polish tank builders designed the 7TP tank based on the Vickers Mk.E. The next step, the development of a fully domestic design, turned out to be too difficult for Polish industry. Attempts were made, but progress did not move past several prototypes. This article discusses 10TP cavalry tank and other experimental designs that did not manage to enter service with the Polish army.
The successor of the TK-S
The development of the TK-3 tankette that later evolved into the superior TK-S was a significant achievement for the Polish army. The design of Major Wladislaw Trzeciak, Captain Edward Karkoz, and engineer Edward Habich satisfied the army's needs in armoured vehicles. About 600 tankettes of this type were built. They became Poland's most numerous armoured vehicle.
At the same time, the future of the tankettes was uncertain by the mid-1930s. They were only suitable for a small number of tasks and their armour protected from rifle fire only at a range of a few hundred meters. The armament was also weak, and placement of the machinegun in a casemate reduced the mobility of fire.
The British reached the same conclusion in the late 1920s. Both the military and the designers of the tankette, John Carden and Vivian Loyd, were skeptical of the vehicle's future. MG carriers vanished from the list of prospective designs. They were replaced with light tanks. The mass of these tanks was only 4 tons (later up to 5 tons), the armour was thicker, the engine was more powerful, but most importantly: they had a turret. This evolution eventually led to the Light Tank Mk.VI, the most numerous British tank at the start of WWII. As for export vehicles, which made up a significant percentage of Vickers' income, they remained at the 4 ton mark. As a result, the tank was called Vickers 4-tonner. This vehicle entered the export market in 1932 with great success. Variants were purchased by Latvia, Lithuania, Switzerland, Belgium, Argentina, and the Netherlands. A number of tanks being built for the Dutch were pressed into British service in 1940. Such a tank can be seen in the Bovington tank museum.
One of the earliest 4-ton tanks was shown off in Poland in 1932. The appearance did not go unnoticed by the Polish military. Colonel Tadeusz Kosakowski, a key figure in the mechanization of the Polish army, proposed a purchase of five such tanks in May of 1933, but the deal was never made. Poland did not have enough money to purchase such expensive things as tanks. However, the idea of a vehicle in the 4 ton class was attractive to the army. It was revisited in 1935. The development of the TKW tankette with a turret failed, and Poland's neighbours, Lithuania and Latvia, had just purchased British 4-ton tanks.
Poland also intently followed the developments of their Swedish partners, where 4-5 ton tanks were being built. The Landsverk L-100 was the first such tank. Initially it was only armed with a machinegun, but the the armament was improved in 1934. Now a 20 mm Madsen autocannon was mounted in the turret. A prototype with a torsion bar suspension was built in 1935. Polish military engineers followed this progress closely.
Eduard Habich, the head of PZInż (State Machinebuilding Factory, Warsaw) headed the development of a Polish analogue to the Vickers 4-tonner. This tank is often called 4TP, but its actual designation was PZInż 140. Three prototypes would be built at a cost of 615,679 zloty.
The project was presented on December 14th, 1936. The tank's ancestry was easy to guess. The characteristic hull with a driver's compartment shifted to the left and engine in the right were reminiscent of the commercial Vickers-Carden-Loyd. The British tank's front transmission, number of road wheels, and return rollers also matched. However, the PZInż 140 was not a copy of the British design. A number of elements made it distinct, such as the superior suspension. The British tank had a Horstmann suspension, while the Polish tank used torsion bars. It was inspired by Swedish designs, but with many changes. The Landsverk L-60 and L-100 had an individual torsion bar suspension, while the Polish tank had bogeys with two wheels each. Hydraulic shock absorbers were added between the swing arms. The engine was also more powerful. The 3.88 L V-8 PZInż 425 engine coupled with a 4-speed gearbox put out 95 hp.
The difference in armament was also noticeable. The British tank had a cramped turret with a single machinegun. A small batch of tanks with 2-pounder guns in a slightly enlarged turret was built for Latvia on special order. Both variants had their own shortfalls: the first had grossly insufficient firepower, the second vehicle was essentially a tank destroyer with no ability to fight infantry. Polish designers followed the lead of their Swedish colleagues, especially since they worked very closely together. For instance, a delegation from PZInz led by Major Karkoz visited Lansverk in late 1936.
A special variant of the Landsverk L-120 reconnaissance tank was developed especially for Poland. It was considered a viable alternative to the PZInz 140. Both Swedish tanks had one man turrets with a 20 mm Oerlikon autocannon. Poland picked a different path. The PZInz would have a one man conical turret with a 20 mm autocannon and a wz.30 coaxial machinegun. The gun mount was similar to the mount on the 7TP and was shifted to the right to make more room for the commander, who also doubled as the gunner and loader. Like the gun, the turret had Swedish roots. The Bofors company was tightly involved in designing both.
The 20 mm autocannon was not the only variant of the PZInz 140. It was clear that tank armour is increasing in thickness, and the 20 mm gun was no longer enough to fight tanks. Habich also designed an alternative variant, known as the PZInz 180. Instead of a 20 mm autocannon, it had a 37 mm wz.36 gun, the same one as the 7TP. This tank would also have a different turret. This variant remained on paper. In the case of the 20 mm gun, it arrived, but very late. Polish designers ended up creating their own 20 mm gun known as the FK-A wz.38A. The first samples of the gun were only available in 1938, so the PZInz 140 was tested without armament initially.
The Polish army had grandiose plans for the light tank. According to the five year armament plan accepted in 1937, 480 tanks would be produced to arm 18 reconnaissance tank companies in infantry divisions. Such vast appetites are explained by the desire to replace the obsolete TK-S and the tank's exceptional characteristics. Even on paper it seemed no worse than its analogues at the time. The tank was low (only 1750 mm in height), mobile, and well armed. The armour reached 17 mm in the front and offered reliable protection against rifle fire. The PzII, the closest analogue of the 4TP, was slower and heavier. Its only advantage was that it could mount a radio.
Habich's tank also had an advantage in observation. It was equipped with Gundlach periscopes, better known as the Mk.IV. The PZInz 140 was also going to serve as a base for the PZInz 152 artillery tractor and the PZInz 160 tank destroyer with a 37 mm wz.36 anti-tank gun. This 4.2 ton vehicle would have a height of only 1600 mm.
Trials of the PZInz 140 began in August of 1937. The tank travelled a distance of 1861 km in a year. The military was generally satisfied with the tank. Its top speed was 55 kph. It was easy to service. There were downsides, however. The suspension travel was too short, such was the price of saving on torsion bars. That was the cost of bogey suspensions that used torsion bars in general. Only the Italians did something similar with their Carro Armato L6-40. The suspension also broke often, but most nations initially had problems with torsion bar suspensions. Another issue was a lack of shock absorbers for vertical oscillations, which made the tank shake.
Trials continued into 1938. The 20 mm FK-A wz.38A gun was installed in the summer. A more powerful 120 hp PZInz 725 engine was also installed during trials. The tank had travelled for 4300 km by May of 1939. Production was being discussed. However, it was not to be, and the start of the war was not to blame. The Polish military itself rejected the tank. Having studied the war in Spain, it became clear that lightly armoured tanks are too vulnerable on the battlefield. The role played by the TK-S and 4TP tanks was going to be filled by tanks closer to the 7TP, but better armoured. As a result, the PZInz 140 tank had no place for it in the Polish army. The tank suffered the same fate as the second tank that was supposed to be used by tank companies within infantry divisions: the 10TP.
Cruiser tank, Polish style
Poland had a Western partner even before their work with Vickers in the face of Walter Christie. The American engineer developed a convertible drive tank for Poland, but it turned out to be a poor design. The second attempt to obtain a convertible drive tank was made in 1929. Captain Marian Rusinski was sent to the USA on behalf of the Military Engineering Research Institute (WIBI). He met Christie and discovered that the US Wheel Track Layer Corporation was working on an improved version of the M.1928 tank named M.1940.
After negotiations, a contract was signed. Christie would produce an improved M.1928 tank for Poland. The cost of the tank was $30,000 and spare parts would cost another $3500. The deadline was 90 days after the contract was signed. Soon after, Christie signed another deal for the delivery of the same M.1940 tank to Poland's greatest enemy: the USSR. The Soviets turned out to be a much more profitable client, and the deadline for Poland's tank slipped. Poland threatened to sue, but all they managed was a refund. This story ended poorly for Christie. In 1936, when he was left with no clients, he offered his help to Poland but was rejected. Poland could manage without him by then, and his latest projects looked very questionable.
The interest in a Christie tank did not die out, but the design was heavily criticized even in the US. On October 14th, 1932, the Ordnance Department prepared a tender for the Convertible Medium Tank T3E2. The winner of the tender was Christie's greatest competitor, American LaFrance. The fire truck company built a very different tank, but it proved to be troublesome, never quite becoming a true replacement for Christie's tanks. Nevertheless, the mention of this tank is no accident. The tank built in Poland was closer to the T3E2, and not Christie's T3. The Polish tank also used a 240 hp American LaFrance engine, which was hardly a coincidence. This was the same engine used on the Combat Car T1E3.
Work on the Polish tank began in 1932 and was based on the materials that Rusinski received from Christie. Since the priority was given to the 7TP, the Vickers Mk.E analogue, work progressed slowly. The WIBI was disbanded in 1934, and the documentation on the «Polish Christie» was destroyed, so little information survived to this day.
Work was relaunched on March 10th, 1935. This time, the project was developed by the Armoured Vehicles Design Bureau (Biuro Badań Technicznych Broni Pancernych, BBT Br.Panc.). The development was led by Major Rudolph Gundlach, another key figure in Polish tank building. The lead engineer was Jan Lapushevski. The project received the index 10TP. Development started out slowly, but was expedited in January of 1936 when the Committee of Armament and Supply (KSUS) approved the project in 1936.
The overall concept of the 10TP tank was the same as Christie's design, but the implementation was closer to the American LaFrance tank. The biggest complaint about Christie's tank was the two man crew. This was changed on the T3E2. Its crew consisted of five men: three in the turret and two in the hull. An assistant driver was added to the driver's right. He was also given a machinegun. The tank became 33 cm wider and a little bit longer. The hull shape changed significantly. All of this was also done on the 10TP. Like the American tank, Gundlach's tank was wider than the Christie tank. The overall width increased to 2550 mm. The hull was also longer, since more space in the driver's compartment was needed. The front of the hull was shorter, like the Medium Tank T3E2, and the front armour received a characteristic step. The hull was partially welded and partially riveted.
The running gear was very original. Like the Christie tank, it had four dual road wheels per side, a vertical coil spring suspension, and a gear linkage between the drive sprocket and the rear road wheel. The design had some original mechanisms, however. The location of the suspension springs was changed. When shifting to wheeled drive, the tank pulled up its second pair of road wheels. A new wider track link was developed, eerily similar to the tracks designed by Christie for the Airborne Tank M1936. The drive sprocket also changed, but it was still similar to Christie's later designs.
The armament was typical for Polish tanks of the time. The turret was taken from the 7TP with no changes. At the time it was entirely satisfactory. There are some guesses that the turret would have been improved in production, but this information cannot be confirmed. The tank also received a Ckm wz.30 machinegun mount. The armament was in line with the standards of the time. By the standards of the mid-1930s the tank also had reliable protection. The front armour was as thick as 20 mm.
The 10TP cruiser tank was an important part of the five year plan adopted by the Polish army in January of 1937. At least 64 of these tanks would be built and sent into motorized brigades. Each brigade would have a company of 16 10TP and a company of 4TP tanks.
Work on the tank dragged on. While the 4TP had entered trials by August of 1937, its «big brother» was only being assembled at the Ursus factory. Assembly was directed by Casimir Gruner, but due to slip-ups it took until June of 1938. Secret mobility trials began in August. The first stage completed on September 30th.
The results were mixed. On one hand, the tank was easy to drive. On the other hand, there were enough complaints about the design even without the constant small defects that were unavoidable in any new tank. The engine chosen for this tank was too weak. It is not known if the Polish military knew about the criticisms aimed at the Combat Car T1E3 by the Americans. The maximum engine power was 240 hp, but it was reduced to 210 hp during practical driving. The 10TP had a mass of 12.8 tons, so even at maximum power output the power to weight ratio was less than 20 hp/ton. In practice, this was only 16.4 hp/ton. For comparison, the PzIII Ausf.A had a power to weight ratio of 16.67 hp/ton, the BT-7 had 29 hp/ton, and the Cruiser Mk.III had 23.9 hp/ton.
The 10TP had the weakest engine of all Christie medium tanks. The top speed on a highway was 34.5 kph and 20.6 kph on a country road. This was considered sufficient, but clearly not enough for a tank of this type. The designers also missed the mark with fuel capacity. The tank only had room for 130 L of fuel, which was far too little considering the consumption of 110 L per 100 km of highway driving.
Trials continued into January of 1939, when the tank covered a distance of 2000 km. The results were disappointing. It was clear that the convertible drive concept was outdated, and the tank's armour was no longer satisfactory. Work on the 10TP ended and Polish cavalry was left without a tank. Poland entered WWII not only without any modern tanks in production, but without even prospective ones. Even if the 10TP was accepted into service, there would be an issue with supplying the engines. It is unlikely that American LaFrance would meet the demand.
Great ambition, little ammunition
Polish tanks that remained on paper are a whole different story. Like Aryan fantasies, which have little to do with actual designs, there are many fictional Polish tanks. For instance, this drawing is often credited to German intelligence and called 14TP. There was never such a tank, but there was a 14 ton Polish tank conceived. There were two different variants proposed.
According to research by Polish historian Janusz Magnuski, work on the 14TP began in late 1938. The cause was the understanding that the convertible drive concept was outdated. The advantages of this design were few, and the tank turned out to be very complicated. The 20 mm of armour was already rather thin. This led to the concept of a 14 ton medium tank. Essentially, this was a fully tracked 10TP with thicker armour. The index 14TP was not used, but the prospective tank's mass was estimated at 14 tons. The increase in weight came from the thickening of the armour to 30 mm. This protected from high caliber machineguns and even from light anti-tank guns at a large distance.
There were two types of engines proposed: one a 245 hp (presumably an analogue of the American LaFrance engine), the other a German Maybach HL 108. Information on this tank is contradictory. On one hand, it is said that a prototype was started. However, in that case it would be mentioned in German documents. It is more likely that the tank remained on paper.
If work on light and small tanks at least reached the prototype stage, then medium tanks became an unreachable goal for Polish tank designers. The first requirements for a medium tank were composed in the summer of 1936. They described a 12-20 ton tank equipped with a 75 mm gun.
The requirements later increased, and development turned into a race between BBT Br.Panc. and KSUS. There is information that Habich was also working on a medium tank, but only a description of doubtful credibility exists. One can confidently say that the index 25TP that is often thrown around has no connection with reality.
As with the light tanks, British tanks were chosen as a starting point. In this case, it was the Medium Tank Mk.III, an unsuccessful vehicle, but a known one among tank builders in the 1930s. Polish designers also carefully watched the T-28, the only medium tank of the early 1930s that crossed the 100 vehicle mark. The concept included two levels of armament: two machinegun turrets that fought infantry and a large center turret with a cannon and a coaxial machinegun. The tanks of the two competing design groups were similar.
The BBT Br.Panc. group led by Rudolph Gundlach designed a tank with armament that did not match the initial requirements. The tank would have a 40 mm wz.36 AA gun (the Polish version of the Bofors gun). The tank also had three ckm wz.30 machineguns: one coax and two in the turrets. An 81 mm mortar would also be used. The tank would be very mobile. Two engines with a combined power of 600 hp would give it a top speed of 45 kph. The armour was up to 50 mm thick. Judging by the drawing, the tank would make use of cast armour.
KSUS developed their tank in two variants. The tank, known as the KSUST, was similar to its cousin from the BBT Br.Panc., especially when it came to the hull. The first variant consisted of a 22 ton tank propelled by an unknown 320 hp diesel engine. The main armament consisted of a 75 mm model 1897 gun. The tank had three ckm wz.30 machineguns, but no mortar. Unlike the seven men in the BBT Br.Panc. tank, this one only had a crew of 6. The armour was also thinner at 35 mm. Theoretically, the first variant of the KSUST would have a top speed of 35 kph. The second variant had a mass of 25 tons, a pair of 300 hp engines, up to 50 mm of armour, and a top speed of 45 kph.
Some fans of Polish tanks even fantasize about heavy tank «projects», ignoring the fact that Poland had no tank factories or engine factories. The only small tank building nation of that time capable of producing a medium tank and nearly launching mass production was Czechoslovakia. This tank, the CKD V-8-H, aka ST vz. 39, also piqued the interest of Poland. As for Poland itself, it could not even manage producing a new generation of light tanks. The most that the army could hope for was foreign purchases. By the fall of 1939 the army obtained about 50 Renault R 35. French medium tanks were of interest, but there were barely enough for France itself. Polish industry could not come up with anything satisfactory.
Poland did get heavy tanks, but only during the war. These were IS-2 tanks supplied to the Polish army by the USSR in 1944-45. A number of medium and heavy tanks were developed in Poland after that, but these were thesis works that did not survive aside from descriptions. As for real tanks, Poland first built T-34-85 tanks under license, then T-54s. Even now, Poland produces tanks based either on their Soviet «heritage» or Swedish designs. Entirely new vehicles either remain on paper or exist only as models.
Translated by Peter Samsonov. Read more interesting tank articles on his blog Tank Archives.
- Następcy TK-S, Janusz Magnuski, Andrzej Kiński, Militaria I Fakty 33;
- Czolg Poscigowy 10TP i Czolg Szturmowy 14TP, Janusz Magnuski , Andrzej Kiński, Poligon 2010/1.