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© Michal Derela, 2015

Polish light tank 7TP


Part I: development, production, description
Part II: service & evaluation


7TP trials at Błędowska desert in Poland

Development - Production - 9TP tank - Description - Specifications - Modelling | Part II: Service - Evaluation

The 7TP was the only genuine tank produced in Poland before World War II, not counting tankettes, which hardly can be regarded as tanks. It was also the most combatworthy armoured vehicle in Polish Army at a time of a German invasion in 1939, and one of icons of pre-war Polish Army. The 7TP was the most advanced of all Vickers 6-Ton tank derivates in the world, and can be considered a Polish design, being a compilation of several foreign licences and own inventions; a far-going development of a basic tank. Despite it was not most modern tank in 1939, but it kept a world's standard as for a light tank class, when this class constituted a mainstay of armoured forces worldwide, and could be a match for any enemy vehicle.

This article is an attempt to sum up most recent knowledge about the 7TP tank. Despite its popularity in Poland, some areas still wait for a thorough complete research (first of all, production and combat usage). On this occasion we also fix some errors, that can be found in new Western (and even some Polish) publications. Note: W marks external links to Wikipedia articles.


Development and production

Background

Twin-turret 7TP on parade in Cieszyn. The crew wears old tank helmets. Note armoured covers for MG water radiators, and a peacetime lynx markings on turrets.
Radio-equipped 7TP tank in Zaolzie, cheered by a crowd - note receiver aerial on turret's roof, an aerial base on turret's side, and a folded aerial on a fender.

After World War I, a basic tank of Poland was the French Renault FT. In the 1920s there started works upon equipping the Army with more modern tank, that could be manufactured in Poland. Experiences of the Polish-Soviet War 1919-1920 proved, that a tank should be a weapon of a manoeuvre warfare, and therefore Poland decided to rely on relatively fast and well armed light tanks instead of slow and heavily armoured infantry tanks. Own designers had not enough experience and that is why the only way was to buy a licence abroad for a good start. New Renault designs M26/27 and NC-2, bought for testing in 1929, were not found satisfactory. The Poles also tried to buy an example of a widely advertised Christie's wheel-and-track tank in 1930, but Christie failed to deliver an ordered example (more in 10TP tank article). Poland eventually decided to buy British light tank Vickers Mark E, also known as the Vickers 6-Ton tank, which was one of the most modern tanks in the world at the outbreak of the 1920s and 1930s. It should be noted, that after designing several own tanks, also the Soviets relied upon the Vickers 6-Ton licence, creating most numerous tank in the world before World War II - the T-26.

In September 1931, Poland bought 38 twin-turret tanks Vickers Mk.E Type A, with a licence to manufacture. Next, 22 of them were rebuilt to single-turret Type B, with a short-barrel 47 mm gun (more on Vickers E in Poland page). It was considered a successful design, although it revealed several faults as well, mainly an overheating engine and thin armour. That is why Poland did not start production of the Vickers Mk.E, but in late 1932 Polish designers started works upon its improvement. The works were carried by the Armoured Weapons' Construction Bureau of the Military Engineer Research Institute (BK Br. Panc. WIBI) in Warsaw. Main designer was Aleksander Fabrykowski, and a whole design was under supervision of Rudolf Gundlach. The designers cooperated with a Studies Bureau of a future manufacturer – PZInż (Państwowe Zakłady Inżynierii - State Engineering Works). The new design was first known as the VAU 33, but soon the official designation was changed to the 7TP (7-tonowy polski - 7-Ton, Polish), despite its weight exceeded 7 tons from a beginning.

The weakest point of the Mark E was its 90 hp air-cooled petrol engine Armstrong-Siddeley, which was prone to overheating. The licence did not cover the engine anyway, as a result of the tank's evaluation in Poland. At an early stage of development it was decided to replace it with a stronger and more reliable water-cooled Saurer Diesel engine, manufactured in Poland under a Swiss licence. This way the 7TP became the first Diesel-powered tank produced in Europe, and one of first in the world (about the same time such engines were introduced to Japanese tanks). Among advantages were: less inflammable fuel, better torque and lower fuel consumption. In fact, the choice of Diesel engine was accidental, as it was the only engine of appropriate power output produced in Poland at that time[note 1]. Its drawback was, that it was quite heavy, despite the Poles had lightened a basic engine Saurer BLD and increased its power output to 110 HP, creating VBLDb variant. The new vertical inline engine and its water radiators, replacing a lying inline air-cooled engine, demanded high rear compartment, which was the most obvious visual difference from the Vickers E and T-26 family. Among other improvements were: thicker and better quality armour (up to 17 mm face hardened plates instead of 13 mm homogenous plates), strengthened suspension and new transmission. The tank was also to be fitted with a modern anti-tank gun, although it had not been chosen at first. Significant details were new small headlights on fenders.

VAU 33 (or V.A.U. 33) stood for Vickers-Armstrong-Ursus, or according to other version, Vickers-Armstrong Ulepszony (improved), 33 for the year. The designation 7TP was derived from Vickers Mk. E, which was often called in Polish documents just a '6-ton tank' (czołg 6-tonowy), and later a '7-ton', or in short: 7T tank, which better corresponded with its actual weight. The designation was often written as 7 T.P. in original documents. Twin- and single-turret variants had no specific designations. In Western publications they are often marked with additional letters: "dw" or "jw", which are abbreviations of Polish words: dwuwieżowy = twin-turret [approximate pronunciation: dvu-vye-zhovy] and jednowieżowy = single-turret [yedno-vye-zhovy]. However, they were not part of name, and such abbreviations are not known in any Polish sources. They might be used for a sake of convenience only, but they should always be separated from the name by a space. The single-turret variant was however regarded a standard one, without need of additional designations.


Development

The first 7TP prototype (it has experimental welded rocker arm and non-standard toolboxes). See a second prototype in newer configuration (as an armoured draisine).
A modified 7TP prototype, with an original Bofors turret.
Early production single-turret 7TP tank (note low muffler).

Two prototypes of the new tank were ordered on 19 January 1933. The sketches were ready by 24 June 1933, but the first prototype was assembled in the PZInż Experimental Workshop only in August 1934. It carried no. 1595 and a nickname Smok (Dragon). It was followed by a prototype no. 1596, accepted by the Army on 13 August 1935 (probably nicknamed Słoń - Elephant). The prototypes still utilized some British parts bought from Vickers. Both were twin-turret, made of mild steel (with possible exception of turrets). Their factory designation was PZInż. 120. The prototypes were intensively tested and the design underwent further improvements. At the same time there were built and tested prototypes of C7P tractor on the same chassis, what was partly responsible for long works.

On 18 March 1935, the first series of 22 twin-turret tanks was ordered. All were twin-turret, utilizing machine gun turrets removed from 22 Vickers E tanks during their conversion to single-turret ones[note 2]. Such armament was a forced solution, since a final turret and gun had not been chosen by then. First series tanks had rear hull plates with two armoured grills, replaced next with less vulnerable solid armoured doors. Also a muffler was modified in October 1936 – unified with C7P tractor, and its position was changed from bottom to top of a rear plate (early mufflers had twin exhausts, late mufflers were shorter and had one exhaust). These changes were not applied to already built vehicles, apart from the testbed Smok, and probably all tanks ordered in 1936 and built in a single-turret configuration still had armoured grills and low mufflers. It is worth to note, that at the same time there was tested twin-turret Vickers Mk.E tank, modified in March 1936 to 7TP standard (no. 1359, so-called V/7TP).

The final configuration was to be a single-turret tank, with an anti-tank gun. Different guns were considered, of 37-47 mm caliber. Some were of Polish design, including 47 mm Pocisk gun and projected 40 mm and 55 mm guns of Starachowice Works, but were mostly unproven. Vickers turret of Mk. E Model B tank was rejected because its short-barrel 47 mm Vickers gun had poor performance against armour. Vickers proposed also a new hexagonal turret with a new more powerful 47 mm gun, but it was also rejected. In autumn 1935, Swedish 37 mm Bofors gun was chosen, since it had been just adopted as a standard towed anti-tank gun for Polish Army, and offered a good performance for that time. Bofors also offered to design a turret, basing upon turrets for Landsverk L-30 and L-10 tanks.

The prototype turret of mild steel was delivered from Sweden only in November 1936 and used to rebuild the prototype no. 1595 Smok in January 1937. The turret had access doors in its rear plate (photo), but the design was modified, and serial turrets, manufactured in Poland, had a rear niche instead, and an upper hatch. The niche could accommodate a radio or additional ammunition, and it also improved turret's balance (not to mention the tank's silhouette). The turret was equipped in Poland with an innovatory commander's reversible observation periscopeW, designed by Rudolf Gundlach, and a periscope sight, for firing on a move (of Zeiss design, produced in Poland). A secondary coaxial armament became a standard Polish infantry water-cooled 7.92 mm wz.30 machine gun (a modified and re-chambered copy of Colt-Browning M1917). The single-turret tank got a factory designation PZInż. 220.

From 1938, some single-turret tanks were equipped with Polish radio N2/C - they were battalion's, company's and platoons' commanders'. The radio utilized a short whip receiver aerial on a turret niche's roof, and 6 m high transmitter aerial of a bamboo stick, mounted to the niche's left side. Probably it was made of two 3.5 m and 2.5 m parts, like in a cart-mounted version. Both were carried over a left fender, apparently with no special frame, and had to be erected manually. With 6 m aerial, it had a range of 10 km for voice transmission and 25 km for Morse code (I suspect, that it was used only when stationery, like in transportable version). With shorter aerials, it could have a range of 8 or 5 km for voice transmission. According to some publications, platoon's commanders had receivers only[10], but it does not seem confirmed. Tanks with radios were also fitted with an intercom for the crew, who were equipped with new type helmets with integral headphones. Only 38 N2/C radio sets were produced for tanks by the war, though not all were mounted in 7TP tanks. Some twin-turret tanks received a radio earlier (probably older RKB/C). In transport position, its pole aerial was carried horizontally, on two high struts between turrets (possibly they were folding rearwards; a rear one might have been an aerial's base). According to memoires, radio communication in 7TP tanks worked well, although its presence was limited to commanding vehicles - the rest of tanks had to follow the commander and watch flag signals.


Production and deliveries

On 18 March 1935, the first series of 22 twin-turret tanks was ordered. First four were built already in 1935, and the rest by spring of following year. Also two prototypes were given to the Army as training vehicles. As for further orders, publications conflict in details regarding numbers and exact dates, and this subject still waits for a proper complete research[note 3]. However, a total number of manufactured tanks – 134 with prototypes – seems established.

Single-turret 7TP tanks on parade in Warsaw on 3 May 1938 - visible differences between main production tanks (second from the right) and early production ones.
Single-turret 7TP tanks on parade in Warsaw on 3 May 1938 (main production). Note a camouflage.

Due to budgetary limits, a policy became to order one company a year, and in 1936 only 16 tanks were ordered. According to part of publications, two were eventually completed as twin-turret, what would bring a total number of twin-turret tanks to 24, and the rest were later completed as single-turret. Then, in 1937 there were ordered 18 7TP tanks, to bring a number of single-turret tanks to two companies. However, according to recent articles by K.Rudy, first there were ordered 18 tanks, manufactured and given to the Army by spring of 1937 without any armament (and apparently with no turrets, which were ordered only in March 1937 for a single-turret variant), and then there were ordered 16 single-turret tanks, for a next fiscal year[note 4].
      Only thanks to sale of four companies of old Renault FT tanks to Republican Spain (fictionally sold to Uruguay and China), a 'big' extra order for a whole battalion of 49 7TP became possible in 1937. A production of such number was however hampered by limited capabilities of factories, which needed development (and tanks had to "compete" on assembly lines with C7P tractors). At the same time there also occurred problems with production of good quality armour plates, ordered from Batory Steelworks for this batch. There were also delays with new turrets, especially, that their armament, optics and radios had to be ordered separately. As a result, first single-turret tanks from earlier orders (14+18 or 18+16 depending on version) were completed only in summer 1938, and from the order for 49 tanks – at an outbreak of 1938/1939.

Polish military estimated in 1937, that a production of 7TP would cease after producing 206 tanks by 1944. At that time, the 7TP was regarded as an interim tank only, and it was hoped, that new, stronger designs would be developed. For a fiscal year 1938/1939, 16 tanks were ordered in June 1938, and they were delivered by summer 1939, as a last pre-war batch. For a fiscal year 1939/1940, 32 tanks were ordered in early 1939, thanks to extra funds (they were meant for the motorized 10th Cavalry Brigade). However, by September 1939, only 11 tanks of this order were completed, and given to the Army after the outbreak of the war (on a contrary to popular misbelief, they were not a strengthened model 9TP). Further tanks were expected only in November 1939, because there were no guns nor optics ready for them, and as a result they were never completed.

There were different bigger numbers given in old publications, but now it is generally accepted, that 132 serial tanks 7TP were produced and given to the Army, plus at least two mild-steel prototypes. Basing upon an information by J. Magnuski, there were 108 single-turret, and 24 twin-turret tanks made, not counting prototypes[note 5] (alternatively, there would be 110 single-turret and 22 twin-turret serial tanks).

Only in summer 1939 orders grew rapidly because of an imminent war, and on 5 and 29 June 1939 there were ordered two batches of 50 vehicles each, and on 8 August 1939 another 50, but it was too late and none could be completed. Their scheduled deliveries were from December 1939 (35 tanks) to June 1940. Starting from the second batch of 50, there were to be a strengthened model (described farther).

Deliveries of serial 7TP
Order yearNumber orderedSerial Nos.Completion
18 March 1935221683-17044 in 1935,
rest by summer 1936 (all twin-turret)
7 February 193616 1705-1720spring 1937 (without armament - possibly 2 twin-turret)
summer 1938 (completed - 14 single-turret, or all single-turret)
193718 1721-1738summer 1938 (single-turret)
March(?) 1937
(extra order)
491739-1764
1765-1787
16 in end of 1938,
rest by May 1939
1938161788-1803summer 1939
193916+161804-1814only 11 in September 1939
total: 132= 22 (or 24) twin-turret
= 110 (or 108) single-turret
Note: This table is based upon works of J. Magnuski, but there are questions as for its reliability, concerning peculiar orders of tanks, number of single- and twin-turret tanks and their serial numbers.
Assembly of 7TP tanks in PZInż factory

7TP tanks were assembled in PZInż F-1 factory in Ursus (former Czechowice) near Warsaw, which also manufactured their engines and transmissions (along with factory F-4), but most parts were delivered by numerous sub-contractors, chosen each time by bids. Armour plates for hulls were manufactured for different batches by steelworks: Pokój in Nowy Bytom, Baildon in Katowice, Batory in Hajduki Wielkie (all in Upper Silesia region), finally in 1939 also by new Zakłady Południowe (Southern Works) in Stalowa Wola. First 50 turrets were ordered in Ostrowieckie Works in Ostrowiec Świętokrzyski, which delivered armour plates (final assembly was in their subsidiary Steam Locomotive Works in Warsaw). The second batch of 58 turrets were ordered in Zieleniewski, Fitzner & Gamper factory in Kraków (plates were made by Pokój steelworks in Nowy Bytom). There is no information where and when further turrets were ordered. Parts of turrets (main bearings) were imported from Sweden (in the first series at least).

37 mm wz.37 guns were made by SMPzA (Stowarzyszenie Mechaników Polskich z Ameryki - Association of Polish Mechanics from America) factory in Pruszków, which also made a towed variant. There were at least 111 tank guns made by September 1939, by two orders: 50 ordered in March 1937 and 61 ordered in April 1938 (one was mounted in a prototype 10TP tank). Only in April 1939 there was another order for 75 guns laid, but it is not clear, if any were completed. Machine guns were made by FK (Fabryka Karabinów - Rifle Factory) in Warsaw.

Radios were made by State Tele- and Radiotechnical Works in Warsaw (according to other version by AVA in Warsaw), and optics by PZO (State Optical Works) in Warsaw. Tracks were made by Lilpop, Rau & Loewenstein in Warsaw.

You can read about service and evaluation of 7TP tanks in part II.



Proposed development - so-called 9TP tank

Polish designers were aware of relatively poor protection of 7TP, and planned its development. One serial tank no. 1766 was experimentally fitted with a new Saurer CT1D Diesel engine, which was to be produced in Poland as PZInż.155. In spite of a lower power output (100 HP at 1800 rpm), it was much lighter (around 600 kg instead of 850 kg). The tank was tested from May 1938, and the engine was considered as better, than the existing one. It was next tested in autumn 1938 with extra weight to simulate heavier armour.

BBT BP proposal for a strengthened 7TP.

Two variants of an improved tank were proposed in April 1939. They are commonly known as 9TP tanks, although this designation apparently comes from a postwar literature, and they were known in original documents just as a strengthened 7TP. More advanced proposal was developed by Armoured Weapons Technical Research Bureau (BBT BP), led by Col. Patryk O'Brien de Lacy. It proposed to use a new welded hull, of a lower profile, with a slanted front plate of the combat compartment. A change in the hull shape was possible due to replacing a Diesel engine with a newly developed Polish 95 hp petrol engine PZInż.725 placed on a right side of the engine compartment (a drive shaft was also moved to right side, so it would be less an obstacle for the turret's crew). The engine had bigger fuel consumption, but its weight was to be only 345-370 kg. The armour was to be up to 30 mm in front and rear (vertical plates), 25 mm on a front slanted plate and the driver's hatch, and 20 mm on sides and turret. Thanks to removing cooling grates from an engine deck, and replacing them with slots in sides, the tank would be more resistant to Molotov cocktails. The driver was to be equipped with a reversible periscope (or two of them, according to [1]). The tank retained weight of the 7TP - 9858 kg, with more even weight distribution on suspension sets. A speed was estimated at 32-34 km/h. Height would be 1988 mm (less by 130 mm).

However, more conventional variant of the PZInż. Studies Bureau, worked by Edward Habich, was apparently chosen to be realized. Its hull shape and construction technology remained the same, as in the 7TP, only armour thickness increased from 17 mm to 40 mm in hull front, from 17, 13 and 9 mm to 25, 20 and 13 mm respectively in sides, and from 15 to 20 mm in turret's sides and to 40 mm in turret's front. Weight also increased to 10 594 kg, so wider 320 mm tracks were proposed, to decrease ground pressure from 0.71 to 0.585 kg/cm². An advantage would be equal weight distribution on front and rear suspension sets, while a weight on the rear set would be even 10 kg lower, than in 7TP (5279 kg in front and 5315 kg at rear instead of 4540 kg and 5325 kg). Speed was estimated at 29 km/h, which was an acceptable decrease, especially, that such was a practical speed of an original tank. An engine was to be lighter 100 hp PZInż.155 (Saurer CT1D) Diesel engine. Also a gearbox would be made of aluminium instead of cast iron. On the other side, there were carried studies on a welded armour, which should decrease a weight of an ordinary tank by 210 kg. It is worth to note, that the Soviets started to equip part of T-26 tanks with an applique armour during Winter War 1940, increasing their weight even more (up to 12 t), without strengthening of an original engine.

An advantage of the PZInż development variant over the BBT BP one was, that it could be put into production quicker, and used a licence-built engine instead of a new unproven one. Therefore, the head of the BBT BP proposed to build a mild steel prototype of his variant utilizing one of early prototypes, and to build one or two strengthened tanks of the PZInż variant, with new armour, within a 7TP batch that was under construction at that time, for further tests. The PZInż works itself proposed to manufacture newly ordered series of 50 tanks already in a strengthened variant, what would cause only slight delay. It is not known for sure, whether these proposals were accepted.

According to common version[1], two prototypes of the PZInż 9TP variant were built by 27 July 1939, but there are no documents quoted, that would confirm it explicitly. It appears certainly a misinterpretation of available documents, and in fact there were no strengthened prototypes made (besides, it would be unrealistic to order armour plates and build two modernized tanks in only three months). The tests were carried with already existing no. 1766 tank with CT1D engine and a ballast, fitted with different transmissions during trials. As a result of tests in 27 July - 3 August 1939 period, a differential from C7P tractor was found more suitable for strengthened tanks. The war spoilt plans of production of strengthened tanks. Some publications suggest, that 11 tanks 7TP of the newest production, received in September 1939, had strengthened armour, but it may only be regarded as ungrounded wishful thinking. Publications also claim, that a new batch of 50 tanks ordered in 29 June 1939 was to have a strengthened armour, what seems plausible, though there are no documents quoted, apart from the PZInż proposal.


Technical description

Armament:

A scheme of a turret arrangement (1 - 37 mm gun, 2 - MG, 3 - telescopic sight, 4 - periscope sight, 5 - commander's reversible periscope).
7TP turret. Upon the weapons' mounting there is a fan. In an open hatch there is a lower part of a periscope visible. Next to the hatch there is a periscope sight cover.

An early transitional model of 7TP tank was twin-turret, armed with two water-cooled 7.92 mm wz.30 MG in turrets. The ammunition was around 6000 rounds (5940, considering 330-round belts?).

Main variant was single-turret, armed with 37 mm wz. 37 (Bofors) tank gun, with a coaxial water-cooled 7.92 mm wz. 30 machine gun. Gun ammunition was standard 80 rounds, mainly armour piercing with a tracer (AP-T). There were also used APHE rounds. It is not clear, if HE shells were used - they were available for towed guns and tested in tanks before the war, but a commander of the 2/2 Light Tank Battalion Cpt. Hajdenko claimed, that his tanks did not receive HE shells.
 Only 4 rounds were stowed in the turret - to the right of the gun, however reportedly the crews stowed extra ammunition in the turret's rear niche in tanks without radio. The rest of ammunition was carried in the hull. Maximum rate of fire was 10 rds/min. Machine gun ammunition was 3960 rounds in 330-round belts, carried in 12 boxes. The MG was to the left side of the gun, and its barrel was protected with an armoured cylinder, as was the gun's recuperator.

Weapons had a telescopic sight wz.37 CA between the gun and MG, and a periscope sight wz.37 CA on a left side of a roof. The periscope sight was based upon Zeiss TWZ-1 design, and could be used on the move, while the telescopic sight was used when stationery only. Both weapons were fired with a gunner's pedal, using a hand switch to choose between weapons. There were crank mechanisms for turret traverse and gun elevation, operated by the gunner.


Armour:

The armour was made of bolted rolled plates, of a face hardened (cemented) armour (in hull) or homogenous armour (in turret and horizontal plates), of different thickness:

According to Soviet measurement, hull sides were 15 mm in the middle and 10 mm at the rear, roof was 11 mm in front part, turret roof was 15 mm apart from the hatch (9 mm). There might be some measurement error, although a difference in the turret's roof is significant.


Construction:

Comparative cross-section of Vickers E and 7TP (early) hull[9].
Destroyed twin-turret 7TP, probably in Warsaw area. Noteworthy is a radio aerial base between turrets. Visible are fans on both sides of an engine.

The tank was of classic construction, with a transmission compartment in front, combat compartment in the middle, and an engine compartment in the rear. The hull was made of rolled armour plates, bolted to a frame. The crew was three. The driver's seat was in front of the combat compartment, on the right side. Before the driver there was a large two-part hatch, with a simple periscope in a vision slot. A vision from the driver's seat in combat conditions was rather poor, and he had no means of side observation (just as in original Vickers Mk.E).

Early twin-turret variant had two identical small one-man "dustbin-style" turrets, each with a hatch above. In this variant, the commander-gunner and gunner were sitting on fabric belts (the commander in the right turret). The turrets had significant box covers atop for magazines of 13.2 mm MGs, that were used in Vickers Mk.E tanks only.

Main production variant had single conical two-men turret, offset to the left side. The commander had his station on the right side, and the gunner on the left side. The commander loaded the gun and indicated targets for the gunner, while the gunner searched for targets, aimed the gun and fired weapons (some publications erroneously claim, that the commander was a gunner, and the second crew member was loader). There was a single hatch in the roof, opening forward, on the right side of the roof, above the commander. The commander had a reversible observation periscope wz.34 G in the hatch. There were also two simple fixed periscopes and two pistol ports in both sides of the turret. A rear niche for a radio had an upward-opening hatch at a rear.

The reversible periscope was invented by R. Gundlach and enabled easy all-around observation for a commander. On a contrary to new Western publication, a lower part of the periscope was not stationery, but it rotated in 180° range (there had been already known artillery Goertz panoramic sights with stationery lower part and crank-operated rotating prism, but they were complicated, one-eye, and apparently slower in area scanning and having narrower field of view). Gundlach periscope acted like a simple rotating periscope to look forward and sideward, what demanded turning head to the sides, but thanks to an additional prism extending down, the commander did not have to turn his head around the periscope to scan the area behind him. It had a 54° field of view. A patent was sold to British Vickers-Armstrong before the war, and the reversible periscope became a standard in further allied tanks, including Soviet ones.

Engine was PZInż. 235 (Saurer VBLDb), Diesel, 6-cylinder inline vertical, water-cooled, capacity: 8550 cm³, 110 HP at 1800 rpm, cylinder bore x stroke: 110 x 150 mm.
  The engine was placed centrally in a rear compartment. Two vertical water radiators with fans were placed on both sides of the engine - the air was drawn by two grills in forward part of a horizontal plate over the engine compartment, and flew out through two holes in a rear part of this plate. In early series it also flew out through blinds in rear doors. The rear compartment had two big doors in a rear side, a small hatch above the engine, two small inspection hatches in side plates and two hatches in a wall between engine and combat compartments. The fuel tank 110 l was placed in forward part of the hull, to the left (earlier publications claimed, that there was an additional 20 l tank, but it was suggested, that it was meant for radiator coolant in fact[10]).

Transmission: dry multi-disc main clutch, drive shaft in a combat compartment (under a cover). Mechanical gearbox: 4 gears forward, 1 reverse. Side clutches with band brakes, operated by levers.

Suspension: drive sprocket in the front, idler in the rear. The tank had a modified patented Vickers paired bogie-type suspension: on either side two units of two bogies with two double wheels each, sprung by cantilever leaf springs. Each suspension unit pivoted on its own axle. In early prototypes only there were tested welded rocker arms, but eventually the tanks had cast rocker arms, like in Vickers. All double roadwheels were the same, steel, rubber rimmed (on contrary to Vickers, in which the last pair was steel only). One track had 109 links. Track width: 268 cm, track ground length: 2700(?) cm, distance between tracks' centres: 2028 mm. Four return rollers on each side. Weight distribution on suspension sets was 4540 kg on front and 5325 kg on rear set.


Camouflage:

In 1936-1937 there was a standard camouflage scheme introduced for Polish vehicles. It consisted of irregular patches of greyish sand and dark brown (sepia) over base color of brown-green. The patches were airbrushed, with soft transitions, their shapes were mainly horizontal. There was not any standard pattern of patches. The interior was sand.

7TP light tank - twin-turreted
7TP tanks in standard camouflage (upper drawig Adam Jońca)
(drawings are in a different technique, in fact both should look similar to the lower one
7TP light tank, 1939

Initially, by 1936, for twin-turret prototypes there was an older camouflage scheme used, also called the "Japanese" one in Poland. Traditional publications claimed, that it consisted of patches in bright yellowish sand, dark green and dark brown, separated with thin black stripes. However, recent publications suggest, that the colours might have been yellowish sand, olive green and light blue-grey (read more on a page on tankettes).


Specifications:

Specifications of single turret variant [twin turret, if different]:

Crew 3
Combat weight 9,900 kg [9,400 kg]
Length about 4600 mm [4750 mm with old muffler]
Width 2400 mm
Height max. 2273 mm [2181 mm]
Height to turret's roof 2150 mm (Soviet measurements)
Track width 268 mm
Tracks centers' spacing 2028 mm
Track ground length 2.7 m? (106.3 in)?
Ground clearance 376 mm
Max. road speed 32 km/h
Road / terrain range 150 / 130 km
(Soviet measurements: 195/130 km)
Ground pressure 0.58 - 0.6 kg/cm2
Fuel consumption 80 - 100 litres /100 km
Wading depth1 m
Max. steepness35°
Crossing ditches1.8 m
Weight to power ratio11.1 HP/ton
Ground pressure0.6 kg/cm²
Fuel consumption (road - off-road) 80 - 100 litres/100 km
(Soviet measurements 57 - 85 l/100 km)



Models

Models of light tanks 7TP:

1/72:
- Modelkrak (Mkt 7202) - 7TP (single turret)
- Modelkrak (Mkt 7203) - 7TP (twin turret)
Polish producer. Fine resin models of 7TP, both variants, from mid-90s. Good detail, high quality resin and white metal for tracks and suspension. Unfortunately, single-turret 7TP has wrong, symmetrically placed gun mounting.
- Mirage (72601) - 7TP (single-turret)
- Mirage (72602) - 7TP (twin-turret)
Relatively new (2002) highly detailed injection kits of Polish producer. You can see preview On The Way.
- First To Fight (PL1939-026) - 7TP (single turret, early production).
- First To Fight (PL1939-0xx - to be released) - 7TP (twin-turret)
New (2015) injection quick build kits by a Polish periodic publisher. Fine details, unfortunately, with simplified suspension.
1/76:
- EXO KIT (7604) - 7TP
- EXO KIT (7603) - 7TP twin turret
Nice-looking resin model. A photo of 7TP twin turret (right) and two Vickers
- Ostmodels (P2) - 7TP (single turret, early production) - in fact it was a prototype only, without a turret niche
- Ostmodels (P3) - 7TP twin turret
- Ostmodels (P6) - 7TP
- Red Star Models (RS 89) - 7TP
- Red Star Models (RS 90) - 7TP twin turret
- Crusader Models (CMB70S) - "7TPjw" - single turret)
- SHQ (PT-1) - 7TP dw
- SHQ (PT-2) - 7TP jw
1/35:
- Mirage (35301) - 7TP
- Mirage (35302) - 7TP twin-turret
Polish producer. Old injection kits. Mediocre quality, no interior, awful vinyl tracks. However, they are worth their low price (about $8).
- RPM (35901) makes separate track links for 7TP, T-26 and Vickers (Polish producer) - this kit is a must for the ones above.


Notes:

1. Assessing Polish capabilities, one should remember, that Poland was partitioned and occupied for over a century before World War I, and (unlike in Czechoslovakia) none of occupants was eager to place its machine or arms industry there. As a result, it had relatively weak industrial base at the moment of regaining independence. Moreover, after the war, priorities were to defend borders and rebuild and unify the country, with a tight budget. So, a choice of engines produced in the country was limited. Same factors also had an influence on a development and production of Polish tanks and other weapons.

2. There were only 22 sets of turrets removed from Vickers tanks, so they could not be mounted on two prototypes and 22 serial tanks (according to Magnuski, even 24 serial tanks). Additional twin turrets might be made of mild steel, for prototypes and possibly two training tanks (there is no information, that armoured turrets for a twin-turret variant were produced in Poland, and it would not even be reasonable, being only temporary solution). It is not confirmed, that any twin-turret tanks were rebuilt to single-turret (apart from the prototype, and unfinnished tanks), what is suggested in some publications (without exact information).

3. The first publication treating on 7TP orders and production in detail was an article by Janusz Magnuski in "Nowa Technika Wojskowa" nr 12/1996 [2]. Unfortunately, despite works by J. Magnuski became classic, these numbers (and some other conclusions) are being criticized as basing partly on educated guesses. Recently there appeared a series of new articles on the 7TP by Karol Rudy, however they only partially cover the subject of production. There is also a booklet by Paweł Rozdżestwieński[10], but it seems to be based upon Magnuski's work. The subject still waits for a proper research and analysis of all available documents, which sadly seem scarse.

4. Unfortunately, publications conflict in details as for numbers and dates of 7TP orders, and it is still not clear. Moreover, dates of establishing orders and of formal orders might differ, what causes further confusion. J. Magnuski claimed, that there were 16 tanks ordered as twin-turret on 7 February 1936 (two of which were eventually completed as twin-turret and 14 as single-turret), then 18 in 1937, and he quoted their serial numbers [2,7]. This version was repeated in a recent booklet by P. Rozdżestwieński [10]. K. Rudy however claims in new articles, that there were 18 tanks ordered in 1936 (FY 1936/37), and then 16 (FY 1937/38), all completed as single-turret. Both theories differ in a number of twin-turret serial tanks - 24 or 22, for a total number of tanks. It might be noted, that L. Komuda wrote in an old booklet[9], that first came an order of 16 tanks, "probably enhanced to 18".

5. Numbers of 108 single-turret (97+11) and 24 twin-turret series tanks appear correct, provided, that J.Magnuski gave a correct breakdown on single- and twin-turret tanks on 15 August 1939 (97 and 24 respectively, not counting prototypes), and a correct information about producing two tanks of the second batch as twin-turret. They also agree with a total number of produced tanks. It is however unclear, if any tanks apart from the first series of 22 were really built as twin-turret, which would not be reasonable in a view of the tank's planned armament, and lack of spare turrets (see note 2). There is one more unclear issue, since in addition to 121 series tanks in units on that date (plus 2 prototypes), there was one experimental tank no.1766 with CT1D engine in the Technical Research Bureau (BBT BP), and it should be one of series tanks.



Sources:
1. Janusz Magnuski, Czołg lekki 7TP, "Militaria" Vol.1 No.5, 1996
2. Janusz Magnuski, Produkcja czołgów 7TP, 1935-1939 r., "Nowa Technika Wojskowa" nr 12/1996
3. Rajmund Szubański, Polska broń pancerna w 1939 roku; Warsaw 2004
4. Karol Rudy, O czołgu polskim raz jeszcze, "Poligon" nr 1/2010
5. Karol Rudy, 7TP - nowoczesny czy nie? [7TP - modern or not?], "Poligon" nr 6/2011
6. Karol Rudy, Czołg 7TP - na miarę skromnych możliwości, "Technika Wojskowa Historia" nr 5/2013
7. Janusz Magnuski, Rajmund Szubański, Janusz Ledwoch, 7TP vol.II, Wydawnictwo Militaria, Warszawa 2009
8. Andrzej Wszendyrówny, Marcin Wodejko: Czołg 7TP w dokumentach Centralnego Archiwum Wojskowego, "Do Broni" nr 1/2009
9. Leszek Komuda, Polski czołg lekki 7TP, Typy Broni i Uzbrojenia No.21, Warsaw, 1973
10. Paweł Rozdżestwieński, Czołg lekki 7TP, Wielki Leksykon Uzbrojenia Wrzesień 1939, No.1, Warsaw, 2012
11. Mariusz Zimny, Udział 1 Batalionu Czołgów Lekkich w walkach o Głowaczów 10 września 1939, Rocznik Archiwalno-Historyczny CAW
12. Mariusz Zimny, Zniszczenie części 2 Batalionu Czołgów Lekkich pod dowództwem kpt. Józefa Rejmana we wrześniu 1939 w relacjach uczestników walk , Rocznik Archiwalno-Historyczny CAW
13. Relacje o działaniach czołgów 7TP w kampanii wrześniowej, Rocznik Archiwalno-Historyczny CAW




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Text copyright to Michał Derela © 2015.