WW2 Polish Prototypes

PZInż. 140 (4TP)

Poland (1937-1939)
Light Recon Tank – 1 prototype

The story behind the construction of the 4-tonne reconnaissance tank in Poland dates back to 1932. The Plan for the Expansion of Armored Weapons, Anti-Tank Weapons and Motorization developed at that time provided for the commencement of work on a modern vehicle of this type in Poland. The 4-tonne tank of the British Vickers company was to be used as a reference for it.

It is worth mentioning that the Cavalry Department was exerting strong pressure to start work on a modern reconnaissance tank. The aim was to equip cavalry units with such vehicles. At the same time, it was decided that 4-tonne tanks would be more effective than the available TK tankettes. The possibility of equipping new vehicles with a 47 mm caliber gun was particularly stressed. Finally, Vickers was asked to present its design. The show took place on 27 October 1932 at the Rembertów training ground.

Vickers Light Tank 4 ton model 1933
Vickers Light Tank 4 ton model 1933 before being shipped to Poland
Source: Leksykon pojazdów mechanicznych Wojska Polskiego 1918-1939, A. Jońca (Edipresse, 2018)

The financial situation in the country following the economic crisis put a stop to any tangible work in this area. It should be pointed out, however, that preliminary studies on a 4-tonne tank were initiated by the Military Engineering Research Institute’s (WBInż, Wojskowy Instytut Badań Inżynierii) Armored Weapons Design Office (Biuro Konstrukcyjne Broni Pancernych) as early as in the financial year 1934/35. However, their results are not known.

The issue returned in 1935, however, when the General Staff, being aware of the low combat value of the manufactured tankettes and armored cars, considered the possibility of buying British 4-ton Vickers tanks for large cavalry units. Eventually, however, they decided to commission the design of a vehicle with similar parameters domestically. This task was given to the PZInż (Państwowe Zakłady Inżynierii, the Polish National Engineering Works) Study Bureau (Biuro Studiów) in 1936.

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Light Reconnaissance Tank – PZInż. 140 (4TP)

The main designer of the vehicle, which would receive the factory designation PZInż. 140, was engineer Edward Habich. During the development of this tank, he used many elements from his earlier design – the amphibious PZInż. 130 tank. The project and its documentation were completed on 16th December 1936 and work was immediately started on building the first prototype. The construction of this new vehicle utilized the best and most recently available solutions observed in similar foreign-built vehicles – the light Vickers tanks developed by the engineers Carden and Loyd, especially the Vickers-Carden-Loyd Light Amphibious Tank (prototypes of which had been demonstrated in Poland) and the Swedish Landsverk 100 (L-100 – for the assessment of which a special committee had been sent to Sweden).


The 4TP chassis utilized an indigenously-designed suspension in the form of torsion bars connected to hydraulic shock-absorbers placed in a horizontal position. It consisted of a front-drive sprocket, a rear idler wheel and two sets of rubber-tired roadwheels on each side of the tank. The two return rollers on either side guided the tracks, consisting of 87 cast single-pin double-wedged links with a width of 260 mm and a pitch of 90 mm.

The crew was housed in a crew compartment on the left side of the hull, with the engine compartment to their right. The crew consisted of a driver and a commander. The driver’s position was in the front of the vehicle with the transmission to his right. In front of the driver, there was a single-piece hatch which constituted part of the front plate with an additional observation hatch in the center with a viewport. The driver also had access to a rotating periscope designed by Polish engineer Rudolf Gundlach. The one-man turret was placed above the crew compartment, shifted slightly to the left in relation to the centreline of the hull. It had a two-door access hatch in the rear and an additional hatch on the roof. The turret itself was operated manually and was supposed to be equipped with another periscope on the roof which could be used by the commander. Series-production tanks were also supposed to be equipped with radio stations.

The hull was built from steel plates which were bolted together – a feature borrowed from the Vickers 4-ton Light Tank which resulted in an increased vehicle weight (by approx. 80-90 kg). Despite popular opinion, the hull was not riveted. The front plates had a thickness ranging from 8-17 mm, the sides – 13 mm, the rear of the hull – between 10-13 mm, the floor – 4-8 mm and the top – 5 mm. The turret was made out of rolled sheet steel with a thickness of 13 mm around the sides and 5-6 mm on top.

The power unit was a newly constructed carburetor engine designed entirely by PZInż. The new power unit was the brainchild of two designers – engineers Jan Werner and Jerzy Dowkontt. They began work on the engine on 1st February 1936. The assembly of the prototype was begun in mid-April and ended on 15th August 1936. The very same day, the engine was mounted on an engine test stand and, after four hours of testing, it reached its planned power output of 95 hp. The first series of these engines, as well as its derivative – the PZInż. 425 – was started soon after. One of these was used on the amphibious PZInż. 130 and another was fitted on the PZInż. 140 asymmetrically relative to the main axis of the hull, on its right side. The engine torque was transferred by the main clutch and the transmission via the driveshaft to side clutches and the drive sprockets in the front of the hull.

Polish reconnaissance tank PZInż. 140 4TP
Polish reconnaissance tank PZInż. 140 (known to the military as the 4TP) after transfer to military representatives on 15th August 1937.
Source: Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)


The tank’s turret was structurally similar to the Bofors turret on the 7TP tank, the only difference being its smaller size. The armament was to consist of a 20 mm autocannon with a 7.92 mm coaxial machine gun (most likely the ckm wz. 30 – an indigenous unlicensed clone of the American Browning M1917 heavy machine gun) or even a 37 mm gun in place of the 20 mm gun. During the construction of the 4TP prototype, the Armored Command, under the order of the Ministry of Military Affairs, was considering arming the tank with a stronger gun, the 37 mm wz. 37 tank gun (the same as one the 7TP).

At the beginning, the use of the 7TP turret was proposed, but it proved impossible due to the turret ring diameter being too large. In July 1937, engineer Edward Habich designed and presented a new, slightly modified variant of the 4TP with the factory designation PZInż. 180 and a modernized turret, with a shape resembling a truncated prism. Compared with the original variant of the 4TP, this version was slightly heavier and larger, and armed with a 37 mm gun, used so far solely on light infantry support tanks.

Rejection and Further plans

The project was examined by BBT Br. Panc. at the beginning of August 1937, even before the prototype was completed. The vehicle’s fate was decided by the fact that the gun could only be operated by one crewmember – i.e. the tank commander. It turned out that the tank commander would be incapable of properly carrying out all of his duties (i.e. commanding the tank, observing, aiming, and loading). Building a larger, two-man turret was out of the question as too many modifications would have to be made to the vehicle. An additional drawback was that only some of the parts of the gun would fit in the proposed turret – the barrel with the breechblock and the hydraulic recoil mechanism; the other mechanisms would not fit in the turret and would have to be specially constructed.

Because of all these drawbacks, the proposal failed. Later on, arming the 4TP tank with a locally-built flamethrower designed by the Sappers Development Office (Biuro Badań Technicznych Saperów – BBT Sap.) and the Institute of Armament Technology (Instytut Techniczny Uzbrojenia – ITU) was considered, but this proposal was also never realized.

Ultimately, the finished prototype, the PZInż. 140/4TP, had a turret adapted to use a 20 mm autocannon and a machine gun. It was never armed because the Solothurn and Madsen guns available at the time were ill-suited to the task and there was no indigenously-designed weapon of this type in the Polish arsenal yet.

Polish reconnaissance tank PZInż. 140 (4TP)
Polish reconnaissance tank PZInż. 140 (4TP) during testing in the BBT Br. Panc. “Autumn 1937” (“Jesień 1937”) rally.
Source: Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)


On 15th August 1937, the PZInż. 140 tank was delivered to the military after factory trials. It was tested in the “Autumn 1937” (“Jesień 1937”) rally along with other prototypes. After its completion, it was sent back to PZInż. for repairs, removal of faults, and technical modifications to the design.

In May 1938, the PZInż. 140/4TP was put through more trials. The members of the committee of military experts decided that, despite several technical shortcomings, the tank was a modern design and, following several improvements, was fit for serial production.

Polish reconnaissance tank PZInż. 140 (4TP)
PZInż. 140 (4TP) during winter trials between 1937 and 1938.
Source: Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)

Further development

The main feature warranting redesign was the suspension. Despite the fact that it worked well and was flexible, the variant used in the prototype was too “soft” – which caused too much swaying motion on its transverse axis. As a consequence, the gun could not be properly aimed while driving, which was always a requirement of Polish tacticians and would be very important for reconnaissance duties. As well as this, individual parts of the prototype’s suspension were made of a not particularly strong material, which caused quite a lot of damage. It was planned that, in the future, materials of higher quality and durability would have to be used.

Fate and Conclusion

The armored development plan for the years 1937-1942, adopted by the Armament and Equipment Committee (Komitet do spraw Uzbrojenia i Sprzętu – KSUS) stipulated the replacement of the TK and TKS tankettes with a 4-tonne reconnaissance tank. The programme expected the production of around 480 vehicles of this type to equip 18 tank reconnaissance companies as part of infantry divisions as well as four so-called Motorised Units (Oddział Motorowy – OM) part of a motorized brigade.

The final trials of the 4TP tank before the start of the war took place in May 1939. After their completion, the tank had driven over 4,300 km without any major malfunctions.

The fate of the tanks was discussed for a long period of time. In the end, the General Staff decided that the time needed to set up production for the tank would cause significant “aging” of the design, especially given the apparent low usefulness of light tank designs following the analysis of the use of tanks in the Spanish Civil War. Ultimately, the tank was never ordered into production.

Polish reconnaissance tank PZInż. 140 (4TP)
Side, top, front and rear view blueprints of the PZInż. 140 (4TP). Source: Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)

The single built prototype of the PZInż. 140 (4TP).

Hypothetical ‘in-service’ PZInż. 140 (4TP) with 20 mm nkm wz. FK-A autocannon and ckm wz. 30 coaxial machine gun.

Both illustrations were produced by the author, Bernard Baker, and funded by our Patreon campaign


Dimensions (L-W) 3.84 x 2.08 x 1.75 m (12.60 x 6.82 x 5.74 ft)
Total weight, battle-ready 4.33 tons (8,660 lb)
Crew 2 (commander/gunner, driver)
Propulsion PZInż. 425, 6-cyl, 95 hp, 22 hp/ton
Suspension Torsion bar, leaf sprung bogies
Speed (road) 55 km/h (34 mph)
Range (road/off road)/consumption 450-240 km (280-150 mi)/60 l/100 km
Armament 20 mm autocannon (proposed Nkm wz.38 FK), 7.92 mm machine gun (proposed Ckm wz. 30)
Ammunition 200 rounds for 20 mm autocannon and 2500 rounds for machine gun
Armor 4 to 17 mm (0.16-0.67 in)
Total production 1 (prototype)


Czołg rozpoznawczy PZInż. 140, Piotr Zarzycki (Wielki Leksykon Uzbrojenia Wrzesień 1939, Tom 141 Prototypy broni pancernej, 2018)
Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)
Leksykon pojazdów mechanicznych Wojska Polskiego 1918-1939, A. Jońca (Edipresse, 2018)
Nowe rozdanie, czyli TKS wersji 2.0, Jędrzej Korbal (Technika Wojskowa Historia nr. spec. 6/17, 2017)
Pojazdy Wojska Polskiego 1939, A. Jońca, R. Szubański i J. Tarczyński (Warszawa: Wydawnictwo Komunikacji i Łączności, 1990)

WW2 Polish Prototypes

PZInż. 130

Poland (1937-39)
Light Amphibious Tank – 1 Prototype

At the end of the 1920s, the well-known tank designers from the Vickers company – engineers John Valentine Carden and Captain Vivian Loyd – built a new, specialized variant of a small reconnaissance tank, an amphibious vehicle known as the Vickers-Carden Loyd Amphibian Tank.

The vehicle did not, however, pique the interest of the British War Office enough to place orders. By the end of 1931, Vickers received permission to export the tank and buyers were found almost immediately. The U.S.S.R. bought 8 tanks (on the basis of which they designed the T-37A and the T-38), Thailand (then known as Siam) bought 2, China bought 29, and the Netherlands ordered 2 for service in the Dutch East Indies. Interest in the tank was also shown by other countries, such as Japan, Finland, and Poland.

Vickers-Loyd Amphibian Tank. Source: Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)

At the same time, Vickers also offered small two-man reconnaissance tanks and tractors for sale, all based around the same chassis. News of the new British designs soon reached the Polish Armored Command. Despite serial production of the TK tankettes and a finalized design for the TKS, the weapons development plan had foreseen the design of a small new light tank with its armament in a rotating turret and a more powerful machine gun, such as one with a caliber of 13 mm or even a 20 mm cannon. The tank was to potentially replace the TK/TKS tankettes in the near future.

For this reason, talks with a Vickers representative on the demonstration of the vehicles were started as early as 1932 in Warsaw. In September 1932, the British company shipped three vehicles to Poland – the amphibious tank, the 4 tonne reconnaissance tank and an artillery tractor, all based on the same chassis. They were demonstrated to representatives from various competent institutions and military authorities. The presentation of the amphibious tank’s capabilities took place in Modlin on 8th October 1932, on the banks of the Vistula near the Military Yacht Club. On 25th October of the same year, all three vehicles were demonstrated in Rembertów, near Warsaw, in which the amphibious tank’s ability to overcome ground obstacles and water hazards was greatly admired by the Polish committee.

As a result of these demonstrations, the head of the Department of Engineering Supply (Departament Zaopatrzenia Inżynierii), Colonel Tadeusz Kossakowski, presented a proposal to the Polish General Staff for the purchase of five 4-tonne tanks and one amphibious tank. These were to be a test bed for further research and models on which to base domestic designs.

The General Staff, however, only agreed to the purchase of three vehicles, but even these were never bought due to a lack of funds. Due to this, it was decided that similar vehicles were to be designed without acquiring foreign templates. The Armored Weapons Development Office (Biuro Badań Technicznych Broni Pancernych – BBT Br. Panc.) laid down the tactical and technical requirements for an amphibious tank and a 4-tonne tank design which was entrusted to PZInż (Państwowe Zakłady Inżynierii, the Polish National Engineering Works). Both vehicles were to be standardised and the components were to be highly interchangeable.

Light Amphibious Tank – PZInż. 130

Armored Command expected the amphibious tank to be used in operations in Eastern Poland, especially in the Polesie region, abundant with swamps, rivers and lakes, where normal tanks would have had difficulties due to the character of the terrain.


The main designer of the PZInż. 130 (as well as the 4-tonne reconnaissance tank – the PZInż. 140) was the head of the Tanks Department of PZInż, Engineer Edward Habich.

Most of the components of the tank were unified with those of the PZInż. 140, including the engine, drive train, suspension and track mechanism (with the road wheels and tracks being of a lighter construction to reduce the overall weight). The turret was taken from the second variant of the TKW tankette and was to house a machine gun, with the possibility of also mounting a 20 mm auto-cannon in the future. The small weight to hull volume ratio, along with the hermetically sealed and the watertight construction allowed for the floatation of the tank. To ensure greater stability while floating, the track covers were built as floatation devices filled with cork. The vehicle was propelled in the water by a screw housed in a special retractable hydrodynamic cover, connected to the control levers and side clutches, and acting as a rudder. The power was transmitted from the engine through the transfer case independently of the momentum transmitted to the tracks, which allowed for the simultaneous movement of both the tracks and the propeller. This made it easier for the tank to drive into and out of the water as well as overcome obstacles in shallower waters.

The PZInż. 130 just before submission for trials – differences between this vehicle and the Vickers-Loyd Amphibian Tank include the modern suspension and Gundlach periscope. Source: Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)

Initial Trials

The design and technical documentation for the tank were completed in Autumn 1936. Work on the construction of the prototype started at the beginning of 1937 and finished in the summer of the same year. After a short series of factory tests, the tank was transferred to the military representatives on 15th August 1937 and demonstrated to officers from various institutions on 2nd October. During the demonstration in Beniaminów, the tank was driven by its designer despite the fact that this had been forbidden by the organisers fearing some unforeseen accident. Fortunately, neither the vehicle nor its designer were hurt during the trial.

From 5th October, the PZInż. 130, along with other prototype vehicles, took part in a test rally under the codename “Autumn 1937” (“Jesień 1937”). The route started in Warsaw and led through Brześć (present-day Brest), Wołkowysk (Vawkavysk), Pinsk, Łuck (Lutsk), Buczacz (Buchach), Stryj (Stryi), Żurawica, Lublin and ended up back in Warsaw with a total distance of about 1,861 km with around half of the route being driven off-road. Additional tests for the PZInż. 130 were carried out on Lake Lubiąż (Lyubyazh) and on the Pina River near Pinsk.

The PZInż. 130 before a water test with visible hydrodynamic cover and screw. Source: Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)

Further Trials and Eventual Fate

The overall evaluation of the tank by the military committee was positive – the power to weight ratio was favorable, the acceleration was good, and the tank could easily drive over rough and marshy terrain. The defects that were found were deemed normal for a newly-designed vehicle and, after the rally, the tank was returned to PZInż to introduce improvements and iron out mistakes.

The next test rally took place in May 1938 and led through the Knyszyn Forest to Vilnius Nieśwież (Nyasvizh) and Biała Podlaska with a combined distance of over 800 km which the PZInż. 130 also managed to complete with positive results. This proved the same in all subsequent tests, all of which the tank managed to complete without any significant failures. The last trial of the tank took place in May 1939 and the prototype drove a combined distance of over 3,500 km (other estimates place it as high as 5,000 km).

Unfortunately, at the same time, the General Staff decided there was no need for such a vehicle, and the prototype was returned to the Ursus test workshop. The reasons given were the lack of production capabilities for such a specialised vehicle, its comparatively thin armor and use of factory time which could be spent on building heavier and better armored tanks. At the outbreak of the Second World War, the vehicle most likely remained in the PZInż factory in Warsaw and in Spring 1940 was transported by rail to Germany, where it was put on display as a war trophy at the Leipzig Trade Fair.

Side, top, front and rear view blueprints of the PZInż. 130. Source: Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)


The tank was marked by a great reliability of movement and an ability to cover large distances at a high average speed. The mechanisms were straightforward and the handling and maintenance procedures were very simple. The vehicle was well stabilized, as a result of which driving the tank did not tire out the crew. However, despite its obvious advantages the tank did not enter mass production due to the fact that it would have delayed the construction of much more urgently needed tanks, such as the 7TP, as well as the design of vehicles with substantially more firepower.

PZInż.130 captured by the Germans, in the winter of 1939/40. Source: Polish amphibious tank prototype PZInż.130,

Illustration of the single prototype built in 1937.

Illustration of a Hypothetical in-service variant with the 20 mm wz. 38 FK-A autocannon.

Illustration of a Hypothetical in-service variant with the ckm wz. 30 machine gun

These illustrations were produced by the Author, Bernard Baker, and funded by our Patreon camapaign.


Dimensions 4.22 x 2.08 x 1.88 m (13.85 x 6.82 x 6.17 ft)
Total weight, battle ready 3.92 tons (7,840 lb)
Crew 2 (commander/gunner, driver)
Propulsion PZInż. 425, 6-cyl, 95 hp, 24.2 hp/ton
Suspension Torsion bar, leaf sprung bogies
Speed (road) 60 km/h (37 mph) – on land
7-8 km/h (4-5 mph) – in water
Range 360-220 km (225-135 mi)/58-66 l/100 km
Armament 20 mm autocannon (proposed Nkm wz.38 FK) (200 rounds) or 7.92 mm machine gun (proposed Ckm wz. 30) (2500 rounds)
Armor 4 to 8 mm (0.16-0.31 in)


Czołg pływający PZInż. 130, Piotr Zarzycki (Wielki Leksykon Uzbrojenia Wrzesień 1939, Tom 141 Prototypy broni pancernej, 2018
Czołgi rozpoznawcze PZInż.-130 i PZInż.-140, Janusz Magnuski (Nowa Technika Wojskowa nr. 11/93, 1993)
Nowe rozdanie, czyli TKS wersji 2.0, Jędrzej Korbal (Technika Wojskowa Historia nr. spec. 6/17, 2017)
Pojazdy Wojska Polskiego 1939, A. Jońca, R. Szubański i J. Tarczyński (Warszawa: Wydawnictwo Komunikacji i Łączności, 1990)


WW2 British Prototypes WW2 Polish Prototypes

Kahn’s Obstacle Ball / Rolling Fortress ‘Tank’

UK/Poland/Mandatory Palestine
1941 – Sketches Only

Kahn’s Obstacle Ball or Rolling Fortress tank, a giant concrete ball-shaped tank, comes from the unlikely source of Mandatory Palestine. Mandatory Palestine is, perhaps, not the first place which comes to mind when considering military inventions, but what it did have was a large number of immigrants, especially Jewish immigrants from Europe, settling there. Seeing his home country of Poland overrun and under occupation, Mr. L. Kahn, a Polish-born engineer living in Palestine in June 1941, decided to send his inventions into the Ministry of Works in Mandatory Palestine for potential use in the war. No doubt he could see in the newsreels or read in the papers the ravages of this new World War and decided to turn his skills to the creation of weapons. His letter, written in June 1941, did not go very far though; his ideas were mostly poorly conceived or impractical and lay forgotten for decades. Of his ideas, it is perhaps his ‘tank’ which by virtue of its novelty is most worthy of remembrance.
Kahn, an engineer working for Technotrade Engineering and Technical Supply, Herzl Street, Tel Aviv, sent his suggestions in on the 16th June 1941 along with sketches and some explanation of the ideas.
Kahn’s is not the only ‘ball tank’. In fact, there were far earlier designs, such as the “Tumbleweed tank”, designed by the Texan inventor A.J. Richardson in 1936. There was also a mysterious German attempt known as the ‘Kugelpanzer’.

Plans for Kahn’s Rolling Fortress and method of towing. The area lined-off in the bottom right includes sketches of his anti-torpedo related ideas. Photo: National Archives of Israel

Spherically impractical

This design by Kahn was in an unorthodox shape for a vehicle, a sphere. Whilst there were other ideas for ‘ball-tanks’ being developed elsewhere at the same time, perhaps none of them were on this scale, which combined the ideas of the ‘ball’ with the size of the ‘big-wheel’ landships. Whereas a big wheel was needed to reduce the high ground pressure of a small wheel, in this case, a giant sphere was needed to reduce the ground pressure of a small sphere. Being big would have other advantages too for an obstacle ball.
This vehicle was to be enormous, 20 to 50 feet (6.1m to 15.2m) in diameter with walls 20 to 50 inches (0.5m to 1.3m) thick made from iron-reinforced cast concrete.
The ball was to be cast and then pressurized with high-pressure steam of 100 lb per sq. in. (6.9 x 105 Pascals) and impregnated with carbon dioxide for several hours to help cure the mix of cement, stone chippings, and sand. There was no rebar added within the mix but it was bound with circular irons to provide support for the concrete body.
Kahn is not clear in his letter as to how he expected a hollow sphere to be cast, so the assumption is that it would instead be cast in two halves and then bolted together across one of these boundary ‘irons’. On the smallest end of the scale, this design is a 6.1m diameter ball with walls just 0.5 m thick which would use approximately 49.4 m3 of concrete weighing about 123 tonnes just for the armor. On the upper end, however, the maths shows what a poor idea it really was, as with a diameter of 15.2 m and walls 1.3 m thick, this would mean over 726 cubic meters of concrete and would weigh not less than 1,800 tonnes.
The reason for the pressurization and carbon dioxide infused concrete is that, according to Kahn, this would increase not just the curing time (the time taken for the concrete to set and harden), but also significantly increase the strength by a factor of 5 to 8 times. Kahn elaborated that using this method his ‘light’ wall scheme just 20” (0.5m) thick provided the equivalent strength of a wall 6 feet (1.8m) thick. As Kahn claimed that this 6’ thick armour would be able to resist the shock from even the largest of enemy guns and howitzers, it is unclear as to why a scheme with walls 1.3m thick would ever need to have been considered.

Inside the Ball

Within the ball, things became more interesting. Behind these very thick concrete armour walls was an internal ‘car’ which, attached along an axis by hollow steel pins to the shell, rotated independently of the shell. Thus, as the ball moved, the internal car rotated inside it staying level regardless of the position of the ball.
There was not, however, a double rotation axis, meaning that this stability was not duplicated when the ball obstacle was to move along a sidegrade. There was to be sufficient space (69m3 min. to 1499m3 max.) within the ball for crew, weaponry, and stores.

Towing the Ball

To move these balls around, Kahn did not foresee an internal engine, but instead, two different methods of towing. One was to use a bespoke carriage trailer which was towed behind a standard truck and attached to the ball by the same axial rotation points. Even at 14.4 tonnes though, this ball would likely have done considerable damage to any prepared road surface and would tax the towing ability of a truck uphill as well as being dangerous on any downwards slope although Kahn did consider the need to brake the axial shaft on this carriage for presumably this exact reason. For the larger idea, no truck was capable of moving such an enormous ball and 15.2m was wider than most roads anyway.
On top of this, Kahn foresaw these balls being attached together to form trains behind a truck with between 3 and 5 hooked together meaning a weight being towed between 369 tonnes and somewhat ambitious 9,000 tonnes.

Illustration of the 23 tonne and 1,800 tonne Obstacle Ball or ‘Rolling Fortress’. Modeled by Mr. C. Ryan, funded by our Patreon campaign.


As a defensive fortress, the idea of these giant balls perhaps had some merit to them. They could be anchored together and would be impassable to vehicles, hard to bridge over due to their shape, and hard to destroy. One advantage and clever feature of the design was the low-grade materials used. Apart from pressurizing the concrete, the castings were at least simple enough along with the irons that it could be manufactured locally in theatre rather than in a factory which would have saved time, money and engineering to focus of other things as well as remove the problems of strategic transport. It was not the only vehicle during the war to use concrete as armour. The Bison mobile pillboxes (truck-based pillboxes) were a similar idea and even some tanks used concrete too, but the scale of the concrete used as well as the shape of the vehicle is what sets it apart.
Multiple balls would be connected together through a simple double-ended bolt passed through the hollow axles, and then with nuts tightened up on the inside drawing the balls together. These balls would then be anchored together firmly whilst still able to rotate and move along a common axis, although Kahn made no mention of moving the balls whilst connected, simply drawing a train of three balls fastened together. After connection as a fortress, these balls could then be armed, therefore not just forming a physical barrier, but a fighting fortress line too, or at least, that was Mr. Kahn’s idea. Smaller balls would be fitted with machine-guns or mortars and the larger ones would be able to take cannons or even a flamethrower with the fuel tank held under the fighting platform in the bottom of the ball, although the actual positioning of the loopholes to fire from was poorly considered. The field of fire from each ball was very tightly constrained by an inability to traverse, meaning no matter how well armed a single ball was, it would be surrounded and overwhelmed. They had to, therefore, rely on flanking supporting fire, and although he foresaw these could be ‘quickly deployed to the front’, did not consider the problem for the unarmoured trucks moving these under fire. Later in his letter, Kahn describes the ‘anti-tank flamethrower’ as firing not through a loophole in the ball, but actually fixed to the axial shaft of the ball and projecting from two nozzles, with one in each direction coming from this mounting point.
Also within the area under the fighting platform was to be a tank of water for cooling the machine-guns, indicating perhaps his thoughts of Vickers water-cooled machine-guns or Maxim guns as the primary armament.
For crew access, there were to be two doors also made from concrete and the same thickness as the walls. They were set at opposite ends at the front and rear, meaning whichever angle the ball was at, one door would face down to allow the crew to escape. The other door would obviously be too heavy to open above the crew compartment and this also meant that there was a good chance that the escape door would face in the direction of enemy fire.

The Tank

Kahn was very thorough in one regard with his idea. He seems to have understood that simply towing these balls together was not possible, or at least was unfavorable, due to enemy fire against the unprotected towing vehicles, and consequently, his unpowered towed concrete ball gained an engine. Kahn did not use the term ‘tank’ to describe this adaption though, instead, he used the term ‘self-moving fortress’.
For movement, it was to use a ‘petrol motor… installed inside with both ends driving a geared cadran or V grooved cadran, with single disengaging drive”.
It is hard to envisage how in the relatively small space provided such a motor would power such a heavy ball across even hard ground, let alone on soft ground, and despite this being, in effect, a ball-shaped tank, it was supposed to drive two internally mounted, circumferential and parallel toothed gear wheels with the motor fixed to a stationary platform so as to drive the gear wheel. Kahn does, later in his letter to the Ministry, describe that the engine could also be a diesel unit. To steer the ball, the drive from the engine was switched from either driving both toothed wheels or to one, which would impart an uneven force on one side of the ball steering it in the opposite direction. Vision was provided by a periscope sticking out of each end of the axle.
The whole idea of this ball-shaped tank was poorly conceived, albeit well-intentioned. The idea was, perhaps, unsurprisingly rejected as impractical by the Mandatory’s authorities on behalf of the British Ministry of Supply.

Other weapons

It is worth noting that Kahn’s other suggestions for weapons to the Mandatory’s authorities also met the same level of success as this ‘ball fortress’. Examples of these were electrified shells and electrical landmines to electrocute tanks; an electrified wire carpet to entangle and electrify tanks; concrete escort boats to protect convoys from enemy torpedoes; the fitting of propellers to the sides of ships spinning at 5,000 to 10,000 rpm to break up torpedoes before they hit; These all fell on deaf ears as ideas, as did his idea for a sound-induced death ray for destroying enemy submarines; an infrared morse code apparatus; a tethered shell for shooting down planes; and a tailless fighter aircraft. The Ministry of Supply evaluated all of these ideas as well and all were considered to add nothing new to knowledge and therefore rejected.


Dimensions (L-w-H) Sphere 20 to 50 feet (6.1m to 15.2m) in diameter
Total weight, battle ready 123 tonnes to 1,800 tonnes
Armor Iron-reinforced cast concrete, 20 to 50 inches (0.5m to 1.3m) thick
Propulsion Petrol or Diesel
Armament Variously water-cooled machine-guns, mortars, cannon, or flamethrower

Links & Resources

Government of Palestine Archive File C/273/41 1941

WW2 Polish Prototypes


Poland (1931)
Armored car – None Built

By the early 1930s, the Polish army still didn’t have any type of reconnaissance vehicle that was truly successful. The main armored car (actually a half-track vehicle) was the wz.28, which had a lot of imperfections, like weak armor and armament. The new wz.29 ‘Ursus’ (as these vehicles were produced at the “Ursus” Mechanical Works in Warsaw) was also far from satisfying. Although the wz.29 was well armed and armored, its maximum speed was too low and it had problems off-road. Moreover, the wz.29 was only produced in small numbers.
A new project was started, with the aim of creating a successful armored car for the needs of the Polish Army. In 1930, the Polish PZInż (Państwowe Zakłady Inżynieryjne – the National Institution of Engineering) company (also responsible for later projects like PZInż 220 – the prototype of the famous 7TP) reached an agreement with the Swiss Adolphe Saurer S.A. company for the production and selling of Swiss cars and trucks under licence. The 6×4 chassis of one of the Swiss trucks was a good basis for the new armored car. The project was developed by the designers at BK Br.Panc.WIBI. (pol. Biuro Badań Technicznych Broni Pancernej Wojskowego Instytutu Badań Inżynierii; Armoured Weapons Construction Bureau of the Army Engineer Research Institute). As the final design was ready in 1931, the new project received the designation ‘wz.31’ – ‘wzór 1931’, ‘the specimen 1931’. This name is also shared with a type of helmet, so it can be easily be mistaken on a list of items for example.

Illustration of wz.31 by Janusz Magnuski – it’s currently the only one picture of this armored car. However, it’s imperfect, as this wz.31 has not 37 mm cannon in the turret and front machine gun in the hull. Photo:

Design and Armament

Unfortunately, today the design of the wz.31 is mostly forgotten, as this project was quickly abandoned during the invasion and all of the wz.31 blueprints were destroyed during World War II. The only existing image of the project is the one created by Polish historian Janusz Magnuski. In his picture, the wz.31 does not have the front machine gun and the turret has no cannon. In Magnuski’s drawing, the wz.31 is looking similar to the German 6-wheeled Sd.Kfz.231 (6-rad) or the Soviet BA-10. However, a number of sources have survived.
The general design was based on the previous wz.29, as it was well armored and armed for its time. The chassis of the wz.31 was derived from a truck created by the Swiss Adolphe Saurer S.A. company. Unfortunately, the exact type of truck is unknown. The vehicle had 6 wheels and the rear two axles were powered by the engine. The car probably had 4 forward gears and one reverse. The engineers designed two types of the engines: a four-stroke, 6-cylinder straight engine providing 100 horsepower and a four-stroke, 6-cylinder diesel engine with 84 hp. Both of the engine types were equipped with a liquid cooling system. They were produced by Saurer. The wz.31 had two driving positions: one in the front and one in the back of the vehicle. Internal communication was provided by an interphone.
The main armament was placed in the turret, which was the same as on the wz.29. The turret had 2 machine guns. One of them was fired through the roof of the turret, providing anti-aircraft fire, while another one was placed facing the rear-left of the turret. The previous wz.29 ‘Ursus’ was also armed with one 37 mm cannon. The weapons were placed asymmetrically, at an angle of 120 degrees in order to provide more space. Moreover, the wz.31 could have had one machine gun in the back of the hull (like the wz.29) and one in the front (with space for a machine gun operator alongside the driver). The machine guns were wz.25s (Polish version of the French Mle 1914 Hotchkiss) and the cannon was also French, the SA-18 Puteaux 37mm.

Wz31 artist impression by David Bocquelet
wz.31 artist impression by David Bocquelet

The rejection

The project of the new heavy armored car was rejected quickly, despite all the mentioned advantages. The army didn’t even bother to build a prototype and so the wz.31 remained only as a paper project. The main reason for the wz.31’s rejection was simple – the cost of building it was too high. One wz.31 cost 160,000 Polish złotys, with 99,000 for armament and zł61,000 for chassis and hull. For comparison, the construction of one TKS tankette cost just zł47,800. Moreover, the quite expensive, but rather weak anti-tank armament of the wz.31 was evaluated as ineffectual. The modern armored car needed a more powerful anti-tank gun, not numerous anti-infantry weapons. The new vehicle was also deemed to be too big and heavy.
There can also be another reason for the wz.31’s failure. In 1930, the heavy armored car was displaced from its role as a scout vehicle by tankettes. The production of the TK-3 tankette started in 1931.
Unfortunately, in 1939, the Army of the Second Polish Republic was still lacking a satisfying armored car, as the wz.34 produced in 1934 still had a lot of imperfections.

wz.31 specifications

Dimensions 7 x 2.08 x 2.6 m (23 x 6.8 x 8.5 ft)
Total weight 7.8 tons
Crew 5
Propulsion Straight (100hp) or diesel (84hp) engine, 6-cyl, Saurer
Maximum speed 55-60 km/h (30 – 37mph)
Armament 37mm Puteaux SA-18 + 4 x 7,92mm wz.25
Armor 5 – 12 mm (0.1 – -0.4 in)

Links, Resources & Further Reading
“Samochody pancerne Wojska Polskiego 1918-1939”, Janusz Magnuski; WiS; Warszawa 1993
‘Pojazdy w Wojsku Polskim – Polish Army Vehicles – 1918-1939’, Jan Tarczyński, K. Barbarski, A. Jońca; Ajaks; Pruszków 1995.
‘Wrzesień 1939 – Pojazdy Wojska Polskiego – Barwa i broń’; A. Jońca, R. Szubański, J. Tarczyński; WKŁ; Warszawa 1990
‘’Broń strzelecka i sprzęt artyleryjski formacji polskich i WP w latach 1914-1939’ A.Kontankiewicz; Wyd. Uniwersytetu M. Curie-Skłodowskiej; Lublin 2003

WW2 Polish Prototypes

The Tanks of Pawel Chrobok

Poland (1940-1943)
Tank/APC – None built

The Enigmatic Colonel Chrobok

Of the many Polish tank designs prior to 1945, those from the pen of Pawel Chrobok are perhaps some of the most unusual. Very little is known of Chrobok, save for a few patents submitted in his name while living in exile in Great Britain during WW2. In 1940 and 1941, Colonel Chrobok of the Polish Free Army, Rothsay, Scotland submitted two designs for a tank/APC hybrid vehicle.

The First Design

Col. Chrobok’s first design was submitted in December 1940 while residing at the Polish Army camp in Rothesay, and titled ‘Improvements Relating to Automobile Gun-Carriages.’ The object of the design was to provide heavy and light ordnance in the tank along with a contingent of foot troops and other portable equipment such as light field guns all in one package.
The front of this first design would concentrate its armament with a wide array of guns consisting of heavy armour-piercing guns, heavy machine guns, flame throwing devices and anti-aircraft guns as thought fit. The entire vehicle was to be armor plated, with special care being given to the crew cabin. The rear troop area of the vehicle was specified to have armored sides and, depending on the requirement, would have either a waterproof fabric cover or an armored roof.
Inside the rear troop compartment were a series of stepped bench-seats arranged longitudinally for troops with a storage area underneath for equipment. The whole area was accessed through a large rear hatch which could hinge either downwards or outwards. The side walls were also intended to open in order to facilitate loading or offloading as the vehicle was also intended to move supplies and the wounded on stretchers. The complete specification for this patent application was complete by 27th December 1941 and it was accepted on 6th July 1942 under Patent number GB 546,287(A).

Colonel Chrobok’s original 1940 design for his ‘Automobile Gun Carriage’


In January 1941, Colonel Chrobok submitted a second and improved variation of his first design, this time titled ‘An Improved Armoured Gun Carriage.’ The most substantial change brought by this improved design was the addition of a small round turret at the rear of the machine, which was to serve as an anti-aircraft gun. A less obvious difference was the addition of two parallel longitudinal firing ports on each side of the troop compartment, permitting the troops to fire from within.

Colonel Chrobok’s ‘Improved Armoured Gun Carriage’ of 1941

A Third and Larger Idea

Colonel Chrobok’s fortunes did not favor his designs and at some point, he left the Polish Army camp by February 1943 and was giving his home address as Du Cane Court, Baltham, London. From here, Colonel Chrobok’s inventiveness continued with a design for fire fighting apparatus in October 1942 and an even more impressive and substantial ‘tank’ in February 1943. This new tank design was intended to fulfil offensive and defensive roles and equipped with, according to Chrobok, “very powerful offensive armament.” With a similar frontal aspect to the previous designs, this design specified that the cylindrical gun turrets (one or more) would be sunk into the body and have a diameter of approximately ⅓ of the overall vehicle width. Specifically, there would be an overlap on the side walls in order to provide buoyancy and the large amphibious design would be propelled in the water by its tracks.

Front view of Colonel Chrobok’s 1943 ‘Improved Armoured Gun Carriage’

Side and top view of Colonel Chrobok’s 1943 ‘Improved Armoured Gun Carriage’ The turrets were arranged so that the hull was stepped, allowing each of the three steps to fire over the other. Each turret was to be equipped with a pair of guns mounted in fixed cradles and elevated or depressed by means of an electric motor. Other armament was to consist of heavy and light machine guns with six of the heavy machine guns located in the angled side walls of each ‘step’ and two light machine guns mounted in the rear of the machine. All machine guns to be held in ball joints for “universal movement.” The “very powerful offensive armament” called for 3.5m long 40-60 mm caliber autoloading guns in the front and central turrets and a 4.5m long 40-60 mm caliber autoloading gun in the rear turret. There was also to be auxiliary armament of hydrogen gas powered flamethrowers mounted in the side walls and a “mine-thrower” in the floor. Each turret was to be equipped with a crew of two and an observer on each deck, one of whom doubled as the tank commander. They were also to be fitted with an electrically operated fan for ventilation.
Cross section of one of the turrets outlining the method for turret rotation and gun elevation/depressionSteering was to be by selective track drive with each track speed being varied independently and allowing the tank to turn. Fuel would be carried underneath the fighting compartment along the bottom of the tank under the engine compartment which was to house more than one engine.

Proposed automotive layout of engines driving the tracks from a twin-engine design.
The armor of the vehicle was to be welded and make use of the angular layout to deflect enemy fire and in keeping with the earlier designs, space was allocated for troops, 75mm field guns and stores as required.

Sectional views of Colonel Chrobok’s 1943 ‘Improved Armoured Gun Carriage’
This final design by Colonel Chrobok didn’t progress past this stage but was approved on 10th December 1943, but subsequently went nowhere. These designs were uncovered by the author as patent archives, previously lost and forgotten. Despite the obvious limitations of the designs they are of historic value as these three vehicle designs were submitted at a time when Poland was being occupied by German forces. Little is known of Colonel Chrobok himself although there is a Wikipedia page for someone likely to be Chrobok but has not been verified.


Colonel Chrobok’s designs were certainly interesting, combining many different ideas but were unworkable. Too large, too many guns and turrets, a nightmare to command and like many projects which try to do everything perfectly, they manage to do no one thing well. They were very complicated ideas at a time when Poland was in German hands and British industry was struggling to produce its own designs. These ideas were complicated, and the financial and human-time costs of developing these into working vehicles was simply not available. It is not known if he ever submitted these designs for official consideration but if he did they did not get very far in the evaluation process. None-the-less his motives were noble, his country was occupied and the need for effective tanks was great. Whoever Colonel Pawel Chrobok was, his designs were both interesting and odd in equal measure and help fill in a black hole in Polish tank history even if now over 70 years later they appear to be outdated and unworkable concepts.


Patent GB546287(A) – 1940
Patent GB546349(A) – 1941
Patent GB562003(A) – 1942
Patent GB557908(A) – 1943
Pawel Chrobok wikipedia

Chrobok ‘Automobile / Armoured Gun Carriage’ specifications 1940-1941

Armament 2 heavy armor piercing guns
Heavy machine guns
Anti-aircraft gun/s
Total production Zero
For information about abbreviations check the Lexical Index

Chrobok ‘Improved Armoured Gun Carriage’ specifications 1943

Crew  6+
Propulsion  twin engines
Armament Twin 40-60mm auto-loading 3.5m long guns in each of front and central turrets
Twin 40-60mm auto-loading 4.5m long guns in the rear turret
8 machine guns (2 in front hull, 2 in each step of vehicle and 2 facing over the rear)
Hydrogen gas powered flamethrowers
Floor mounted mine thrower
Total production Zero
For information about abbreviations check the Lexical Index

Pawel Chrobok’s original 1940 ‘Automobile Gun Carriage’ design – Illustrated by Jaycee Davis (Amazing Ace)

Pawel Chrobok’s 1941 ‘Improved Armoured Gun Carriage’ design – Illustrated by Jaycee Davis (Amazing Ace)

WW2 Polish Prototypes


Poland (1939)
Medium/Cruiser Tank – 1 incomplete prototype

Sources and lack thereof

The 14TP (14-Tonne-Polish) is an obscure and scarcely documented Polish prototype tank designed in the late 1930s, but likely destroyed before it was completed during the German invasion.
Most of the information regarding the 14TP comes from Janusz Magnuski, a Polish historian. The earliest mention of the 14TP in his work (to our knowledge) is in his 1964 book, Wozy Bojowe 1914-1964 (Combat Vehicles 1914-1964). Most of the information in this article either comes directly from Magnuski’s work or from articles based on his work. Almost all available articles on the 14TP typically do not reference primary documents. Original sources from the Polish Central Military Archive are mentioned in the “Czolg Poscigowy 10TP” (10TP Cruiser Tank) article by Tomasz Koch from the 1997/1 edition of the Militaria Polish magazine, but they are not publicly accessible and cannot be verified.
The sources mentioned in the “Czolg Poscigowy 10TP” (10TP Cruiser Tank) article by Tomasz Koch in Militaria 1997/1
The sources mentioned in the “Czolg Poscigowy 10TP” (10TP Cruiser Tank) article by Tomasz Koch in Militaria 1997/1
This lack of available primary sources demands caution and scrutiny when discussing the 14TP project (especially given the growing trend of fake design and dubious information regarding Polish tanks with connection to online tank games).
However, there are certain indications that the 14TP prototype did in fact exist. The project, as described in most sources, is plausible and in-line with the general Polish armor design tendencies. In contrast, some of the modern fake designs that are circulating around the Internet appear to have been created with the express intent of featuring in online tank games, with all the associated exaggerations and disregard for historical design trends.
Furthermore, Janusz Magnuski is a reputed and respected historian, and there is little reason to suspect him of having fabricated the 14TP.
These being said, it is the author’s opinion that the 14TP was a real project, however some of the information should be taken with reservations until primary sources emerge from the Polish archives.
The only publicly available, possibly original source relating to the 14TP appeared in 2009 on the forum. It is a photo of a document bearing the stamp of the Polish Central Military Archive (CAW) and features the Czołg Lekki Polski (Light Polish Tank). The vehicle strongly resembles the 10TP, and the specifications presented match the claimed ones for the 14TP, including the Maybach 300 hp engine, the 14 tonne weight, 50 km/h speed, 30 mm maximum armor and armament. However, the values for the weight and the speed of the vehicle indicate possible tampering, either on the document itself or afterwards. It is possible this is a contemporary change too but only examination of the actual document would clear this up.
The document showing the Czołg Lekki Polski. The values for the weight and the speed show signs of possible tampering.
The document showing the Czołg Lekki Polski. The values for the weight and the speed show signs of possible tampering.


According to Magnuski, the 14TP was designed simultaneously with the 10TP “convertible” tank. However, in contrast to its lighter ‘brother’, the heavier 14TP was designed from scratch as a tracked-only tank, without the ability to run directly on its wheels.
A traditional tracked chassis allowed the designers to give up the complicated systems made necessary by the convertible drive. As the changed chassis was stronger, the 14TP tank could be made heavier. A 14-ton weight was recommended for the tank, with a maximum of 35 mm of armor and a maximal speed of approximately 50 km/h. Later, the maximum armor value increased to 50 mm. For comparison, the lighter tank 10TP had 20 mm maximal armor.
Two line drawings supposed to be the 14TP - Source: Poligon magazine, 2010/1
Two line drawings supposed to be the 14TP – Source: Poligon magazine, 2010/1
The 14TP project was carried out by designers from the Biuro Badań Technicznych Broni Pancernych (BBTBrPanc, Armored Weapons Technical Research Bureau) and Państwowe Zakłady Inżynierii (PZInż, National Institution of Engineering).


In order to propel the 14-ton tank to a top speed of 50 km/h, the 14TP needed a powerful engine in the 300-400 horsepower range. The American LaFrance petrol engine, used in the 10TP, could not reach these requirements. The Polish PZInż R.W.A. was a candidate but was still in testing at that time, so its operability was under question.
The designers instead decided to buy a suitable engine from Nazi Germany. The purchase of the Maybach HL108 engine, as used by the Sd.Kfz.9, was discussed between Polish and German representatives, but the negotiations were supposedly hindered by Germany. By September 1939, this matter was still not resolved and the 14TP apparently never received an engine at all.
The Maybach HL 108 engine
The Maybach HL 108 engine

Illustration of the 14TP by Jarosław Janas


The main armament specified for the 14TP was the 37mm wz.36 cannon which was the primary Polish anti-tank weapon of that time. The wz.36 gun was based on a gun produced by the Bofors Swedish company and, in 1936, Poland purchased a large number of the guns and a license to produce them locally.
The wz.36 cannon in its towed version. The wz.36 cannon in its towed version.
The wz.36 cannon in its towed version.
The wz.36 cannon in its towed version.
The 37mm wz.36 cannon was the main armament of 7TP light tank, as well as for the 10TP and a few other vehicles. During the 1939 September campaign, it was still a very effective weapon, and able to effectively combat any of the German tanks of the time.
However, Polish designers, according to Magnuski, also planned an alternative armament, the 47mm wz.39 gun. The wz.39 was a new weapon with its only prototype built in April 1939, but the plans to equip the 14TP tank with it remained at the blueprint stage.

The two versions of the 47 mm wz.39 gun – Source: Wielki Leksykon Uzbrojenia T.108: Prototypy Sprzetu Artyleryjskiego cz.1
The anti-infantry armament of 14TP originally consisted of two 7.92 mm wz.30 machine guns. This was an unlicensed copy of the American Browning machine gun and also used on the 7TP, 10TP, TKS and TKW prototype tankettes.
The Polish wz.30 machine-gun
The Polish wz.30 machine-gun
This light armament was later planned to be replaced with two 7.92 Typ C machine guns, but never implemented.
A line drawing of the Typ-C 7.92 mm machine-gun prototypeA photo of the Typ C machine-gun
The 7.92 mm Typ C machine-gun prototype


The 14TP prototype was allegedly approximately 60% finished when the Second World War began. When the invasion started, the prototype was located in the Experimental Workshop of BBTBrPanc and PZInż in Chechowice, near Warsaw. All plans and the uncompleted prototype of the 14TP were likely destroyed, probably by its designers, who wanted to save it from capture by the German invaders. As a result, both the design and precise specifications of 14TP are lost.
‘What-if’ reconstruction of the 14TP tank by WoT forum user Raznarok.
A very liberal ‘what-if’ reconstruction of the 14TP tank by WoT forum user Raznarok. The vehicle sports the 37 mm wz.36 gun, the Typ C 7.92 mm machine-guns and a turret with a widened rear section. This drawing is an artistic interpretation of the 14TP based on what little information exists.

The Polnischer Panzerkampfwagen T-39

Any discussion of the 14TP is usually accompanied by a drawing of the ‘Polnischer Panzerkampfwagen T-39.’ It allegedly comes from a German Abwehr (Military Intelligence Service) report regarding developments of the Polish tank industry. Thus, it has been claimed to be the 14TP and is the most widely used when discussing the 14TP.
However, the Polnischer Panzerkampfwagen T-39 bears no resemblance to the 10TP, on which the 14TP was most likely based. Also, a document has appeared, claiming to be the original Abwehr source. This document is certainly fabricated. The T-39 and its drawing are also almost assuredly fakes.
The Polnischer Panzerkampfwagen T-39 drawing that is often cited as the 14TP. It is almost certainly a fake.
The Polnischer Panzerkampfwagen T-39 drawing that is often cited as the 14TP. It is almost certainly a fake.


“Czołgi Wojska Polskiego 1919-1939” by Janusz Ledwoch (Wydawnictwo Militaria, Warsaw, 2015)
“Czolg Poscigowy 10TP i Czolg Szturmowy 14TP”, Poligon magazine, 2010/1
Modelstory Polish website about the 14TP Polish forum thread discussing various designs, including the 14TP
14TP on Wikipedia

14TP specifications

Dimensions (assumed) 5.4 x2.5 x2.2 m (17.1 x8.2 x7.2 ft)
Total weight, battle ready 15 tons (33,000 lbs)
Crew 4 (driver, co-driver, commander, gunner)
Propulsion 10 l V12 Mayback HL 108, 300 hp
Suspension Christie suspensions (coil springs, bars)
Speed (road) 50 km/h (30 mph)
Armament 37 mm Bofors wz.36 or 47 mm wz.39 gun
2x 7.62mm wz.30 or 2x 7.92 mm Typ C MGs
Armor Up to 50 mm (1.97 in)
For information about abbreviations check the Lexical Index
Failed Tanks WW2 Polish Prototypes


Poland (1927)
Medium tank – 2 prototypes

The WB-10 (sometimes written W.B.10) was the first tank designed and built in Poland. It was also one of the only Polish interwar armored vehicles that was completely original. Without drawing inspiration from foreign vehicles, as was the case with the TK tankettes or 7TP. The WB-10 was planned as a successor to the French-bought Renaults FT. Unfortunately, the WB-10 was a complete failure and the whole project landed in the dustbin of history.
Very little information has remained to this day. Three photos exist which are speculated to be of the WB-10 prototypes, somewhere near Warsaw in 1939.
A supposed drawing of the vehicle is also widely circulated on the internet, but it is not compatible with the vehicles seen in the two pictures. It has become clear that the vehicle in the drawing is actually the Landsverk BT.150 II, a successor of the Swedish Landsverk L-5, in no way connected to the Polish WB-10.
It is highly important to stress that most of the information with regards to this vehicle should be treated with a healthy dose of skepticism until primary sources can be discovered and shed more light on the curious WB-10.
A Polish Renault FT. This was the only tank in Polish service when the WB-10 was designed - Source: Derela Republika
A Polish Renault FT. This was the only tank in Polish service when the WB-10 was designed – Source: Derela Republika

A new Polish tank

In 1925, the only tanks available to the Polish army were the Renault FTs received in 1919. They were still usable but needed modernizations. The WWI era FT had a lousy maximal speed, a weak armament and had problems with terrain obstacles.
The Polish Army started negotiations with Great Britain over the purchase of British Medium Mark D tanks, but this endeavor failed. Finally, the Army decided that the Polish arms industry should become independent and build its own tanks. So, in 1926, the Polish press announced a contest for a project of a new tank.
The requirements for the new 12-ton design were quite strict
• All-around armor strong enough to resist the 13 mm bullets from 50 meters
• Front and sides strong enough to resist 47 mm shells from 500 meters
• One 47 mm (or higher caliber) cannon
• One 13 mm anti-aircraft machine gun
• One 7.92 mm machine gun for anti-infantry use
• Periscopes giving 360° of vision around the tank
• Engine with a warming and cooling system
• Smoke screen device
• Radio with 10 km range
• Maximal speed ≥ 25 km/h
• Operational range ≥ 200-250 km
• Possibility to ride on 35°- 40° slopes
• Possibility to cross 2.2 meters ditches, 0.8 meters walls and to ford 1 meter of water
• Average ground pressure ≤ 0,50 kg/cm2
The contest entries were underwhelming. As the tank concept was still a novelty, tracked vehicle designers and engineers were rare in Poland. Only three projects were reported – and only one project, the WB-10, designed in cooperation by two companies: S.A.B.E.M.S. and WSABP “Parowóz” (“Steam Locomotive”) received the green light.
Moreover, the two companies designed two alternative versions of the vehicle and built two models powered by small electric engines. They were designed by professor Ludwik Tadeusz Eberman of the Lviv Polytechnic, who was working for WSABP.
Until this contest, the “Parowóz” company built steam locomotives and S.A.B.E.M.S. was building engines.
Unfortunately, little to no information about the two other competitor projects are available. They were supposedly armored cars or wheel tanks, not true tanks. One of them supposedly had four axles and the second one just two.

Rise and disappointment

The new project was rather modern and complicated for the time. It was a wheel-cum-track tank, so it had the possibility to change its way of running depending on the terrain, with the wheels being preferred on roads and the tracks on rougher terrain.
Some sources claim that the WB-10 was also amphibious and could lower or raise its hull. The latter claim probably refers to how the wheel-cum-track system worked, and not that the vehicle had a sort of hydropneumatic suspension. Moreover, the chassis could be used as basis for a special tractor.
The army ordered a prototype of the new tank. The construction took a significant amount of time, but two tanks were eventually ready for testing. Regrettably, the WB-10 came to be a giant disappointment. The vehicle suffered a lot of breakdowns due to its complicated design and mistakes in the project. These caused problems with driving the vehicle and according to other versions the WB-10 was not even able to start the trials. These failures brought about the quick cancellation of the WB-10 project. The new Polish tank was rejected.
After this failure, the negotiations with Great Britain were restarted, resulting in the acquisition of the Vickers 6-ton and the eventual creation of the 7TP.
The Vickers Mark E that became the next Polish tank - Source: Derela Republika
The Vickers Mark E that became the next Polish tank – Source: Derela Republika


The fate of the WB-10 prototypes is unknown. They were probably just scrapped after the trials or sent to some army station as technical oddities. However, it is almost guaranteed that they were finally destroyed.
As the WB-10 was a total failure, it faded from memory quite rapidly. After the destruction brought about by World War II, a lot of the information about the vehicle was lost.

The design

The WB-10 was a wheel-cum-track tank. It had four wheels which could be lowered, raising the tracks of the ground. If the tank was to go cross country, the wheels would be raised and the vehicle would use its tracks.
Nothing is known about the engine. However, the designer Prof. Eberman also worked on diesel-type engines, so it is possible the vehicle had such an engine. The WB-10 was probably a massive and slow tank, typical of the period. If it indeed had any amphibious qualities, it is unknown if it had any propellers or if it used its tracks to paddle the water.
The contest requirements suggest that it was able to fit a 47 mm or higher caliber cannon. However, nothing else is known of it.
The 13 mm machine gun is also unknown. The French 13.2 mm Hotchkiss M1929 machine gun was designed years after the WB-10. The 13 mm caliber was most probably just an approximation for 12.7 mm, the typical caliber for anti-aircraft machine guns. The 7.9 mm machine gun was probably the 7.92 mm Hotchkiss wz.25. This was a widespread Polish machine gun that was an improved version of the French Mle 1914 machine gun.
The prototypes could have been painted in khaki camouflage – this color was typical for Polish prototypes (like the Renault TSF or 4TP).
The two supposed WB-10 tanks, next to a number of FIAT trucks. The soldiers unfortunately obscure a lot of details on the vehicle - Source: Odkrywca forum
The two supposed WB-10 tanks, next to a number of FIAT trucks. The soldiers, unfortunately, obscure a lot of details on the vehicle – Source: Odkrywca forum

A reconstruction of the tank claimed to be the WB-10, based on the available photographs - Illustrator: Jarosław Janas.
A reconstruction of the tank claimed to be the WB-10, based on the available photographs. Unfortunately, the illustration is no longer believed to be accurate – Illustrator: Jarosław Janas.

Another reconstruction of what the WB-10 might have looked like. Source: WoT Forums, user Tanohikari

Photos and pictures

Two photos of two unknown vehicles have appeared on the Polish website. It is claimed they were taken near Warsaw in 1939. The photos apparently come from the Patton Museum collection.
They present two groups of soldiers next to some FIAT 621 trucks and two big, mysterious tanks. These vehicles do not resemble any known tank in Polish service or anywhere else in the world. Their old-style design suggests that they may be the WB-10 prototypes, left in some army station.
The vehicle in the foreground is visible in both pictures and, although the soldiers obscure it to some degree, its design can be observed. The background tank is barely visible in one of the pictures. It seems as though it differs from the first tank.
The first tank is lacking its wheels, which were most likely removed or reused on some other vehicle. However, in one of the photos, a large bar is seen protruding from the side of the vehicle. This was most probably one of the attachment bars for the wheels. Both the vehicles are large and tall and almost certainly too heavy to be amphibious. The first vehicle has a large decagonal turret, with no hatches or other elements visible.
The other photo of the same vehicle, claimed to be the WB-10 - Source: Odkrywca forum
The other photo of the same vehicle, claimed to be the WB-10 – Source: Odkrywca forum
A third photo has emerged on the forum. It seems to show one of the same tanks, but at a later date. The general shape and details indicate that this is indeed one of the unknown tanks supposed to be the WB-10. The vehicle appears to have been partially dismantled, missing its turret and quite a few of its armor plates. However, the two supposed wheel supports are clear in this shot. Also, this is the only photograph of the front of this vehicle.
The third photo of the supposed WB-10 tank.
The third photo of the supposed WB-10 tank.
The Czech HPM magazine, in its nr 9/2001 edition, published some schematics of a tank claimed to be the WB-10. However, the drawings in the magazine are of the Landsverk BT.150 II, a successor of the Landsverk L-5, a Swedish wheel-cum-track prototype. The schematics don’t resemble in any way the two tanks in the photos.
The supposed WB-10 design, as presented in the Czech HPM magazine. It bears no relationship to the tanks in the photos and no sources are indicated
The supposed WB-10 design, as presented in the Czech HPM magazine. It bears no relationship to the tanks in the photos. It is actually a Swedish Landsverk BT.150 II – Source: SP15
Landsverk, the vehicle actually in the Czech magazine drawings The Swedish Landsverk BT.150 II, the vehicle actually in the Czech magazine drawings – Source: SP15

One of the other designs?

The Polish writer Janusz Magnuski mentions in his book “Wozy bojowe” (Wydawnictwo Ministerstwa Obrony Narodowej, Warsaw, 1964) that there was also third tank prototype built for the contest. It is possible it was one of the other two wheel tanks that competed against the WB-10. This third tank was designed by professor Czerwiński (no other information known about this person) and failed just like the WB-10.
Some Czech sources claim that only one WB-10 tank was built and the second prototype was another vehicle, called the WB-3. The WB-3 was apparently tested in 1927 and the WB-10 prototype was built as an alternative. According to this theory, the WB-10 tank was never completed. Also, only the WB-3 was a wheel-cum-track vehicle, while the WB-10 only had tracks. However, no Polish source mentions the WB-3 tank.


“Wozy bojowe” by Janusz Magnuski (Wydawnictwo Ministerstwa Obrony Narodowej, Warsaw, 1964)
“Czołgi Wojska Polskiego 1919-1939” by Janusz Ledwoch (Wydawnictwo Militaria, Warsaw, 2015)
On the Odkrywca forum

WW2 Polish Prototypes


Poland (1936)
Tankette – 1 prototype


While working on the C2P light unarmored carrier, Polish technicians from BBT Br. Panc. (pol. Biuro Badań Technicznych Broni Pancernej ; the Armored Weapons Technical Research Bureau ) started a project to build a TKS tankette with the undercarriage of this unarmored vehicle.

The C2P artillery tractor. This vehicle is now at the Polish Military Hardware Museum in Warsaw – Photo:
The new undercarriage was very similar to that of the classic TKS, but it had new side clutches and bigger wheels at back. BBT Br. Panc. converted one TKS (number 1510) to the new chassis, as a prototype It was named TKS-B (“TK ze Sprzęgłami Bocznymi” – “TK with Side Clutches”) (sometimes written TK-SB or TK-S-B). These were the only differences between the original TKS and the TKS-B. The whole construction was still derivative from the Carden Loyd tankette of the 1920s.
From the specifications point of view, the TKS-B was very similar to the TKS.
TKS-B was armed with the wz.25 Hotchkiss (Mark 1925; modification of French Mle 1914 Hotchkiss) machine gun – it was the normal weapon for all Polish tankettes in this time. However, as the photos show, no machine gun was mounted on the prototype.
TKS number 1510 was one of the first produced vehicles this type, so the prototype had the same armor arrangement as the first series (thinner than later series). However, the armor was made of regular iron, and not armor-grade materials.
Additionally, the prototype had no the periscope, typical for the regular tankettes.


The TKS-B was tested in the summer of 1936 and the trials were successful. In comparison with the regular TKS, the new machine had a higher maximal speed (from 45 to 50 km/h), was easier to maneuver and had overall better ride properties. Moreover, it was easier to drive and had better fuel consumption. The manufacturing company planned to convert all existing TKS tankettes to the TKS-B standard by exchanging of the undercarriage with the new one.
By 1936, production of tankettes in Poland had stopped, so conversions were the only way to realize the TKS-B project. The Senior Officers in the Polish Army rejected this idea. The cost of all these modifications was too big. One conversion cost about 10.000 zł, while one standard TKS tankette cost 47.800 zł. Furthermore, tankettes had been considered as only temporary vehicles, without future.


The TKS-B concept was rejected as unprofitable in favor of light tanks. At the same time, there were also some plans to realize the two light tanks projects: 4TP (PzInż. 140) and swimming tank PzInż. 130. These machines could have been the successors of the TK-3 and TKS tankettes.
However, the TKS-B vehicle was not scrapped. The single TKS-B prototype was used for other conversions; ultimately, in April 1937, it was reworked into one of the two TKS-D tank destroyer prototypes.


Plastic model company Mirage Hobby created two myths about the TKS-B: that it was armed with a 20mm FK-A rifle and that the TKS-B was used against the German invaders in September 1939. Neither of these is true. The prototype of this machine had already been converted into the TKS-D when the FK-A rifle was introduced and War World II had started. The TKS-B in its sandy-green-brown camouflage and with a 20mm gun is only a “what-if” concept.


On the Derela Republika website

TKS-B specifications

Dimensions 2.64 x 1.78 x 1.32 m (8’8”×5’8”×4’4”)
Total weight 2.63 tons
Crew 2
Propulsion Polski FIAT 122AC/B 6 cyl, 42/46 hp
Speed 45-50 km/h (31 mph)
Range – Consumption 110-180 km (70-110 mi) – 70 l/100 km
Armament Hotchkiss wz. 30 7.92 mm (0.3 in) machine-gun, 2400 rounds
Armor Front: 6 – 10 mm
Sides: 5 – 8 mm
Back: 5 – 8 mm
Top: 3 – 6 mm
Bottom: 4 mm
Total production 1 prototype

The TKS-B prototype with it's 3-tone livery - Illustration by Jaroslaw Janas.
The TKS-B prototype with its 3-tone livery – Illustration by Jaroslaw Janas.

The only surviving photo of the TKS-B tankette.
The only surviving photo of the TKS-B tankette. The lower side of the vehicle is larger, with a different drive sprocket, extended mudguards and a far bigger idler. It is difficult to the untrained eye to distinguish it from a regular TKS. Photo:

The TKS-B was converted into one of the two TKS-D tank destroyer prototypes.
The TKS-B was converted into one of the two TKS-D tank destroyer prototypes. Here it is paraded in front of the President of Poland, Ignacy Moscicki, the King of Romania Carol II and Prince Michael of Romania. Photo –

The artwork of the Mirage Hobby model kit of the TKS-B. It is incorrect. The TKS-B never mounted a 20 mm cannon. By the time that particular gun was developed, the TKS-B had been converted into the TKS-D.

WW2 Polish Prototypes


Poland (1938)
Cruiser Tank – 1 prototype

The Polish Christie Tank

Poland chose to produce tankettes (The TK3 and TKS), derived from the Carden-Loyd Mark VI, more because of economical constraints than tactical choices. But there was also a real interest for another Vickers-Armstrong product of 1930, the Vickers 6-ton light tank of which 38 Type A and 22 Type B were ordered in 1932-33. This model served for a local development by the Ursus company, soon known as the 7TP. This was just one of several tanks models that the Army was looking on. Another was an American one, the Christie tank. Indeed, the 7TP was given the same old bogie suspensions systems of the Vickers 6-ton which didn’t made the cut in terms of speed. Whereas the American concept was soon copied by neighboring USSR and Great Britain for its Cruiser Mark III.
10TP without tracks
10TP without tracks in its original configuration. Narrow tracks were carried, strapped on the catwalks.
The 10TP, however, was born much earlier as the Military Institute of Engineering Research (Wojskowy Instytut Badań Inżynierii, WIBI) sent Captain Ruciński in a mission in the US to legally acquire a Christie M1928 tank plus its blueprint and license. But the deal never materialized. Therefore it was not before the early 1930s that the WIBI Tank Design Bureau took charge to create a local tank inspired by the Christie M1928 and M1931 after data, leaflets and notes taken by Captain Ruciński.


The WBI design bureau was liquidated in 1934 and the project was interrupted by the more urgent 7TP. It was taken over by the newly established Design and Testing Centre of the Armoured Forces, but most of the original documentation has been lost or destroyed so it started almost from a blank page and on 10 March 1935 the 10TP officially started under supervision of Captain Rudolf Gundlach (the famous periscope designer). His team also comprised engineers Jan Łapuszewski, Stefan Ołdakowski, Mieczysław Staszewski, Kazimierz Hejnowicz and process engineer Jerzy Napiórkowski. The design was advanced enough to be officially approved and included by the Armament and Equipment Committee (Komitet do spraw Uzbrojenia i Sprzętu, KSUS) in January 1936 to the 1936-42 armament projection plan.
It was specified to be given to four newly formed tank battalions and two motorised cavalry brigades. The final prototype was built by Experimental Workshop (WD), attached to the Ursus complex near Warsaw (PZInż), supervised by Captain Kazimierz Grüner. Because of the foreign engine and mechanical parts, delays amounted and the delivery did not occur before July 1938, it was ready eventually for tests on August, 16. Secret runs started under the supervision of the Trial and Experiment Department in the Bureau of Technical Studies on Armored Weapons headed by Captain Leon Czekalski. Trials stopped on 30 September to correct several minor defaults at the WD unit. Other long trips started from 16 January 1939 achieving a 2000km crash course on 25 April. Then it was completely dismantled at WD to check the wear on particular parts and assemblies and do extra corrections. Were detected and noted an above normal wear of the gearbox and clutches, excessive roadwheels and tracks fatigue, insufficient engine cooling and greater than expected fuel consumption.

Design of the 10TP

Externally, only the large roadwheels betrayed some connection to the Christie design. In fact, the 10TP was certainly not a copy of the Christie M1931 as the Soviet BT series was. The hull was significantly larger to accommodate two men side by side in the turret and two in the hull front (driver and co-driver/MG-gunner). Armour thickness was the same to the front, sides and back at 20mm, and 8mm on the bottom and top. Compartmentation was standard, with a rear compartment for the main engine, which was eventually a 12 cylinder American La France petrol engine which developed 210HP (245 stated by the manufacturer), coupled to a 5 gear mechanical gearbox. The tracks (one on two was teethed, double pin) had smaller links, more durable and made for a quieter ride. There was also a specific link hooking system. New drive sprockets (rear) were designed. Most importantly the the second pair of roadwheels were raising by using advanced hydraulic servomechanisms for steering. Both this and the hooking system were new and unproven, and caused many teething problems.
10TP suspension scheme
10TP suspension scheme
Top speed was around 50-75 km/h which was certainly less than the BT series (almost 90-100 kph), due to a lower output and heavier weight. Range was 210km on roads but fell to 130 in off-road conditions with a 130 l capacity. The two-man turret, protected by 16mm slopes was the same model used on the 7TP, housing a high-velocity 37 mm Bofors wz. 36 coupled with a coaxial 7.92 mm Ckm wz.30. The bow machine gun was of the same model, but its watertank was encased in an armoured mantlet and massive ball mount. There were leather straps on each side to carry the alternative tracks stored on the catwalks.

10TP illustration
Rendition of the 10TP by Tanks Encyclopedia, based on the profile photo, March-April trials of 1938

10TP by Bernard “Escodrion” Baker


Eventually, a demonstration allegedly took place before the general staff (perhaps in May 1939). At that stage the idea was no longer to have a convertible (wheeled vehicle/tracked) model, to get rid of all the dual system complications and stick to a track-only model. The spare weight could be then reallocated to improve armour thickness. Therefore, the whole project shifted towards a new model, the 14TP tank. The fate of the 10TP is not known unfortunately. It could have been cannibalized to create the 14TP or stored, or conditioned to take part in the desperate fight in November. The 10TP would have been however comparable with the British Crusader and its 37mm Bofors was able to deal with most German tanks up to the Panzer IV.

An article by David Bocquelet


The 10TP on wikipedia
The 10TP on derela.republika
Blueprint, by Janusz Magnuski

10TP specifications

Dimensions 5.4 x2.5 x2.2 m (17.1 x8.2 x7.2 ft)
Total weight, battle ready 12.8 tons (25,600 Ibs)
Crew 4 (driver, co-driver(MG gunner), commander, gunner)
Propulsion 6 litre 12-cyl Am Lafrance, 210 hp, 16.5 hp/ton
Suspension Christie suspensions (coil springs, bars)
Speed (road) 70 km/h (44 mph)
Range 320 km (130 mi)
Armament 37mm Bofors wz.36, 2x 7.62mm wz.30
Armor 8 mm to 20 mm (0.3-0.8 in)


10TP, tracks mounted (credits m.derela)
10TP, tracks mounted (credits m.derela)

10TP, profile view (credits m.derela)
10TP, profile view (credits m.derela)

10TP rear view10TP stranded after trials, Radzymińska Street in Warsaw, 25 April 193910TP being tracted near Warsaw 25 April 1939
10TP stranded after trials, being tracted in Radzymińska Street, Warsaw, 25 April 1939.