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Cold War Brazilian Armor

CCL X1 Pioneiro

https://www.tanks-encyclopedia.com/images/drapeaux/brazil_r.jpg Brazil (1973)
Light Tank – 52+1 prototype Built

Up until 1967, Brazil was dependent on foreign states for armored vehicles. Throughout and in the aftermath of World War 2, Brazil would receive large numbers of cheap armored vehicles from the United States, including the M3 Stuart and the M4 Sherman, as it had entered the war on the Allied side in 1942. In fact, Brazil had not undertaken any tracked armored vehicle design since 1932, and those had only been conversions of tractors and cars into armored vehicles during the revolutions of 1924, 1930, and 1932.

Between 1932 and 1958, the Brazilian Armed Forces created a solid basis of technical institutes from which it could educate technical and research personnel. In turn, these helped the Brazilian automotive industry in developing their own automotive parts and helped in opening laboratories for the manufacturers. In 1967, Brazil set up a plan for the country to become more self-sustaining as a country and militarily. The flow of US materiel had decreased because of its entanglement in the Vietnam War, and after a study, Brazil recognized external dependence of arms suppliers as a serious problem for its political power in South America.

As a result, Brazil developed the first tracked vehicle meant for serial production, the VETE T-1 A-1 Cutia, and developed a range of wheeled vehicles, such as the VBB-1, EE-9 Cascavel, and the EE-11 Urutu. The Army engineers who had started most of these projects had now finally gained enough experience to start undertaking the development of tanks. Like the previous wheeled vehicle projects, the engineers started small. They first set on remotorizing readily available M3 Stuarts, and then started developing the vehicle that became known as the X1 light tank. The X1 was a modernization of the Stuart which was armed with a low-pressure 90 mm gun and would be developed into an entire family of vehicles.

The X1.
Source: Blindados no Brasil

Designation

A commonly occurring mistake is that the X1 and the X1 family are referred to as the X1A. This designation was never used by the Brazilian Army, nor anyone in Brazil. The two authorities on Brazilian armored vehicles (Expedito Carlos Stephani Bastos and the Tecnologia & Defesa Team (Hélio Higuchi, Paulo Roberto Bastos Jr., and Reginaldo Bacchi)) never refer to the X1 as X1A. In addition, Flávio Bernardini, former co-owner of the bankrupt Bernardini S.A. Indústria e Comércio, also refers to the vehicles and the family as X1, and not X1A. This is important, since Bernardini was one of the two main companies to work on the X1 Pioneiro.

The Brazilian Army itself also never referred to it as the X1A either, designating it as the Carro de Combate Leve X1 Pioneiro (CCL X1 Pioneiro) (English: Light Combat Car X1 Pioneer), or more officially, as Viatura Blindada de Combate – Carro de Combate MB-1 (VBC CC Medio Bernardini-1) (English: Armored Fighting Vehicle – Combat Car Medium Bernardini-1). The closest Army designation to X1A would be the VBC CC MB-1a, but this vehicle was the X1A1. It is also good to note that the Brazilian Army was heavily influenced by the US Army from WW2 onwards, and as a result, it would be somewhat illogical for them to designate vehicles as X1A, as their American equipment did not do this.

The X1 designations originate from Lieutenant-Colonel Pedro Cordeiro de Mello, the leader of the project. He was the one who designated the X1, and most likely designated the following vehicles as X1A1 and X1A2, and subsequently nicknamed them as Carcará, a type of indigenous crested bird.

A Carcará hawk.
Source: https://www.britannica.com/animal/caracara

The first mention of an X1A is found in documents from the US. Specifically, a document on Worldwide Tank Fire-Control Systems published on November 1st 1983, 10 years after the first X1 was built. This report was written by the Directorate of Intelligence, the intelligence branch of the CIA. In this document, they refer to the X1A, X1A1, and the X1A2. They further mention that these vehicles were rebuilt M3A1 Stuarts by Bernardini, and were armed with 90 mm guns.

From there on, the X1A designation was used in Jane’s Light Tanks and Armored Cars of 1984, which more or less solidified the designation outside of Brazil. This name was then taken over by other people, and as a result, this designation became common on the internet. The overall lack of knowledge on the X1 family designations can be seen throughout the entire X1 family, as the X1, X1A1, and X1A2, are frequently mixed up. A factor that might have caused this misconception in the first place is the lack of relatively easy obtainable sources from Brazil in English. Most sources are in Portuguese and/or not easy to find. In addition, only in October 2019 did the first source in English appear on the Brazilian Stuarts, which was written by the Tecnologia & Defesa team (Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives).

Genesis

With the Second World War intensifying in Europe, the United States sought to improve their territorial and continental defense against potential invasion. Among this strategy was the arming of South American countries, which were ill-equipped to effectively defend their coastlines. One of these countries was Brazil, which, at that time, operated 5 Renault FTs and 28 Fiat-Ansaldo CV-33/35s. Brazil also realized the obsolescence of its Army, and subsequently took this opportunity to not only acquire modern equipment, but also gain American help in building Brazil’s industry. During World War 2, Brazil would significantly increase its steel production and start producing military equipment. It would also reorganize its Army, with the help of the US, into a modern fighting force. In return, Brazil would deliver war materiel to the United States, it would join the war on the Allied side and participate in combat. Brazil entered the war in 1942 and would participate in the Battle of the Atlantic and send an expeditionary force, called the Smoking Snakes, to fight in Italy.

With Brazil’s participation in World War 2 and its position on the American continent, they were able to acquire American equipment under Lend-Lease. Brazil got their first 10 M3 Stuarts somewhere between early August and September 7th 1941. Brazil received a total of 547 M3 and M3A1 Stuarts. Besides the M3 Stuart, Brazil also acquired 104 M3 Lees, and 53 M4 Shermans (the only South American country to receive the M4 through Lend-Lease, as the US was not that willing to Lend-Lease Shermans to South American countries).

An M3 Stuart of the 3rd Batalhão de Carros de Combate Leve (BCCL) (English: Light Combat Car Battalion), in the 1940s.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivative

Genesis

By the late 1960s, the Brazilian M3 Stuarts were worn out and needed to undergo extensive maintenance. With the US fighting in Vietnam, the availability of cheap and modern vehicles was drastically reduced for countries like Brazil. Due to the amount of M3 Stuarts available in Brazilian stocks, the ease of maintenance, low operational costs, the strategic benefit of light tanks in the South American terrain in the case of war with Brazil’s neighboring countries, and the aforementioned US involvement in the Vietnam War, Brazil did not only extensively maintained the Stuarts, but later selected them for extensive modernization which would become the X1.

An M3 Stuart of Brazil.
Source: https://i.pinimg.com/originals/d6/a1/b8/d6a1b8f1db6b9e421131fe3915a406d8.jpg

The operations to maintain the Stuarts started in the late 1960s under the name Plano Impere, (English: Empire Plan or Plan Empire). The conception of Plano Impere started in 1968, with the reassignment of Colonel Oscar de Abrue Paiva to the 1st Batalhão de carros de Combate Leve (1st BCCL), (English: 1st Light Combat Car Battalion). Colonel Paiva was not happy with this reassignment, as it felt like a step back in his military career. The selection of Colonel Paiva for this assignment was not a coincidence. Paiva was a skilled motor mechanic and the perfect candidate to bring the first BCCL up to standard. Paiva demanded that with his reassignment, he would receive enough funds to revitalize all the 17 M3 Stuarts of the 1st BCCL. He would only receive the funds to fully revitalize 5 Stuarts.

With the 5 Stuarts revitalized, Brazil had decided that it would gift some M3 Stuarts to Paraguay. Since the 5 Stuarts from the BCCL were only recently fully overhauled, they were selected to be sent to Paraguay. Before they arrived there, they were tested by the Parque Regional de Motomecanização da 3a Região Militar (PqRMM/3) (English: Regional Motomecanization Park of the 3rd Military Region). These vehicles performed very well and the quality of the overhaul was of a very high standard. With the successful overhaul of the 5 M3 Stuarts, Colonel Paiva managed to secure the funds he needed for the revitalization of more of his Stuarts, and would set Plano Impere in motion.

The Parque Regional de Motomecanização da 3a Região Militar (PqRMM/3) (English: Regional Motomecanization Park of the 3rd Military Region) started gathering Stuarts from around the country to recondition the vehicles. The Stuarts would receive overhauls to the engines, tracks, radio, electrics, and receive new manuals. During the early and mid 1970s, the best preserved and revitalized vehicles received an ‘A’ or ‘R’ on the sides of their hulls, with the A standing for Aprovado and the R for Rejeitado, (English: Approved and Rejected). The approved Stuarts would be sent to the Parque Regional de Motomecanização da 2a Região Militar, (PqRMM/2) (English: Regional Motomecanization Park of the 2nd Military Region), from where they would be converted to the X1. The rejected Stuarts were scrapped, as the X1s and M41 Walker Bulldogs would replace the M3 Stuarts from 1971 onwards.

An approved M3 Stuart.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivative

In 1969, an Israeli delegation visited the 1st BCCL with the intent of buying old equipment they could use. Although the delegation was only interested in a single M5 half-track, which would not be sold, and Brazil was only interested in selling the Stuarts, which would not be bought, the Israeli delegation did help in the idea of modernising obsolete equipment.

The Parque Regional de Motomecanização da 2a Região Militar

Parallel to the efforts of Colonel Paiva to overhaul the M3 Stuarts together with Plano Impere, the PqRMM/2 team took it to another level and started looking into potentially upgrading the M3 Stuarts. From 1968 onwards, the PqRMM/2 team was tasked with the localization of old vehicles through nationally produced components, and the development of new or improved armored vehicles. The first step was the re-motorization of vehicles such as the M8 Greyhound and half-tracks with nationally produced diesel engines.

With the success of these projects, the PqRMM/2 team went to phase two. During phase two, they would develop their own nationally produced wheeled vehicles for the Brazilian Army. The results of these developments became the VBB-1, the EE-9 Cascavel, and the early concepts of Urutu. They would also start setting up contacts with private companies, which could help the PqRMM/2 team with the manufacture of the vehicles, and eventually carry the projects over to the companies. Of these companies, three stood out, Engesa, Bernardini, and Biselli. While Engesa would be focussed on the wheeled vehicles because of their boomerang suspension, Biselli and Bernardini would be the companies to take on tank building. Another step of phase two was the start of the Centro de Pesquisa e Desenvolvimento de Blindados (CPDB) (English: Centre for the Research and Development of Tanks). The CPDB was a study group of Army engineers which analysed the possibilities of locally produced tanks. The first goal was to develop a new family of light tanks, using the M3 Stuart as its basis.

The CPDB and the PqRMM/2 would start the development of the new family of vehicles in the early 1970s, like they did in phase one. They would remotorize the Stuarts with a nationally produced engine, replacing the Continental W-760-A radial or Guiberson T-1020-A Diesel engines. Three engines were selected to be tested in the M3 Stuart: the Deutz F8L 413 V8 229 hp diesel engine, the MWM TD 228 V8 266 hp diesel engine, and the Scania-Vabis DS-11 A05 CC1 6-cylinder in-line 256 hp diesel engine. Each of these engines was mounted in an M3 Stuart.

The Deutz engine was rejected because it had low torque and required ventilation slits on the side of the hull, which would allow water and mud to enter the engine compartment. The MWM and Scania engines were both very large and required a redesign of the hull. Both Stuarts were lengthened with SAE 5150 steel provided by the Companhia Siderúrgica Nacional (CSN). Of the remaining two engines, the MWM engine was the best, but due to commercial reasons, the Scania-Vabis engine was selected.

The three remotorised M3 Stuarts.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivative

The lengthening of the hull provided a couple of challenges to the PqRMM/2 team. The first challenge was bonding the newly welded SAE 4140 steel bay for the engine to the existing hull. The Brazilian engineers did not have experience in mating such large pieces of steel together, and did not want to consult foreign countries on this issue. If they had welded the steel plates in a more or less conventional manner, the large plates would start to warp due to the heat. The solution was a three-step welding plan: the first step was heating the welded steel plates with a blowtorch, then they would simultaneously start welding the structure on both sides of the steel plate, and they would finally protect the weld with a thermal cover.

The second challenge was that the rear idler shifted 30 centimeter (1 foot) to the rear because of the extended rear. The solution was using the 18-ton M4 artillery tractor suspension. An advantage of this was that the 18-ton M4 suspension was an overall better suspension than the Stuart suspension, and it shared components with the M4 Sherman, which made it a good logistical option. The 18-ton M4 suspension was copied by Bernardini, a company which played an important role in the development and production of the X1, together with the IPD technicians. The suspension would receive some alterations to match local requirements and the tracks were produced by Novatracão. Novatracão was previously responsible for the development and production of the first run-flat tyres in the country.

An 18-ton M4 artillery tractor towing a 155 mm Long Tom.
Source: https://nl.wikipedia.org/wiki/M4_Artillerietrekker#/media/Bestand:M4-HST-tows-155mm-Long-Tom.jpg

The X1 project begins

With the successful remotorization of the M3 Stuarts, and the subsequent suspension change, the CPDB started to look at further improvements in 1973. From there on, more companies would get involved in the construction of the X1. The improvements that were looked into, on top of the remotorization, were improved armament, new electrical systems, and new instrument panels. The 37 mm cannons on the M3 Stuarts were not only obsolete, but also at the end of their lifetime. Crews increasingly had more trouble with the cannons. The decision on the most suitable armament for the X1 was quickly made.

Initial sketch of the X1.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

In the same year, Engesa had trialled the EE-9 M1, which was armed with a 37 mm, in Portugal. Portugal liked the vehicle, but considering they already had the AML-90 in service, they suggested Engesa should mount the AML-90 turret, known as the H-90 and armed with the 90 mm D-921 gun, and then return to trial it again. With Engesa already using the low-pressure 90 mm gun which would be used for the Cascavels for the Brazilian Army as well, the CPDB engineers decided that the low-pressure gun, with its excellent HEAT performance, was the way forward from both a firepower and a logistics point of view.

There was an issue though. The H-90 turret, which had 16 mm (0.6 inch) of frontal and 8 mm (0.3 inch) of side and rear armor, did not meet the requirements of the CPDB. The French company called SOFMA, which sold these turrets and guns, refused to sell them separately. As a result, the negotiations were short and the Army bought both the turrets and the gun, and subsequently ditched the H-90 turret. A total of 53 H-90 turrets and guns were bought, of which one was used for the Cascavel. Work on the new light tank began on June 28th 1973, after authorization from the Diretoria de Pesquisa e Ensino Técnico (DPET), (English: Army Research and Technical Educational Board).

The CPDB and Bernardini S.A. Indústria e Comércio started designing a new turret which could mount the 90 mm gun and meet the armor requirements of the CPDB. Initially, Biselli would develop and build the turret with the CPDB, but due to internal issues and a lack of materials, Bernardini took over the turret project. The new turret was constructed from 25 mm (1 inch) SAE 4140 plates from the CSN. With the 25 mm plates, the X1 turret would be able to withstand .50 machine gun fire at a range of 200 meters (218 yards). Even though the H-90 turret was ditched, the components it used and its concepts were copied into the newly developed turret, designated BT-90.

The Bernardini Factory and the BT-90 turrets.
Source: Blindados no Brasil

The original turret ring diameter of 1.4 meters (4.6 feet) of the Stuart was too small. The turret ring was increased to 1.6 meters (5.25 feet) to mount the new BT-90 turret. The BT-90 turret would later receive some improvements, like the installation of periscopes designed by DF Vasconcelos S/A (who previously had developed the periscopes for the VBB-1), and would be redesignated as the BT-90A1 and become the production version of the X1 turret. The BT-90A1 turret differed in a few ways from the BT-90 apart from the periscopes. Some changes include the installation of a machine gun mount and the integration of the vision slits in the turret instead of periscopes on top of the turret. The BT-90 and BT-90A1 turrets would both use the hydraulic turret drive of the M3 Stuart. An interesting detail is that a BT-90 inspired turret with 90 mm gun was built by Engesa and mounted on a Cascavel, while another Cascavel mounted a BT90A1 turret, made by Bernardini, armed with 37 mm. These turrets were supposedly part of a bid between Engesa and Bernardini on which of the companies would manufacture the turret for the EE-9 in the future.

EE-9 Cascavel with BT-90 inspired turret.
Source: Engesa Operational Manual

Bernardini and Biselli

For the construction of the X1, multiple parties and companies were involved. The two most important companies which built the X1 were Bernardini and Biselli. Both companies manufactured truck bodies and value transport vehicles at the time, and came in contact with the Brazilian Armed Forces by manufacturing trucks for the Brazilian Marine Corps and the Army. Since both companies had some experience in the manufacture of armored vehicles, and with Bernardini being a manufacturer of safes and armored doors, they were requested by the Brazilian Army to help build the X1. Although Biselli would never fully commit to the project, which would result in later issues with the vehicle and eventual departure from a later project, Bernardini would commit and eventually become the tank counterpart to Engesa’s wheeled vehicles.

Company/Army Component(s)
United States The M3 and M3A1 Stuart
Biselli Hull extension, engine installation, equipment installation, and track mounting
Bernardini Turret and suspension
CSN Steel armor
Novatração Tracks
DF Vasconcelos Periscopes
Scania-Vabis Engine
PqRMM/2 Stripping of the Stuart, revision of differential and transmission, radio installation, and testing
PqRMM/3 Overhaul and selection of M3 Stuarts

Construction process of the X1

The construction of the X1 prototype and all subsequent vehicles was more or less done in the following order.

The PqRMM/2 would receive the overhauled Stuart from the PqRMM/3. They would unmount the turrets, and recover the transmission and differentials for revision. The hull and revised transmission and differentials were sent to Biselli. Biselli would extend the hulls, mount the Scania engine, install the revised transmission and differential, install the copied 18-ton M4 suspension produced by Bernardini, provide the vehicle with tracks from Novatracão, and finally install electronics and instrument panels. The hull would then be sent to Bernardini, where the BT-90 turret (or BT-90A1 for the production turret) produced by Bernardini was installed on the hull. The completed vehicle was returned to PqRMM/2, which installed the radio and secondary armament, and finally test drove it for 200 to 300 kilometers (124 to 186 miles) and fired 6 rounds with the low-pressure 90 mm cannon.

The X1 hulls at the Biselli factory.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivative

As previously stated, work on the X1 prototype began on June 28th 1973, and was completed in about 2 months. If this included the extending of the hull and the mounting of the new engine is unknown. It is possible that the PqRMM/2 team used the Stuart which was used to test the Scania engine to save time. The prototype, named X1 by Colonel Cordeiro de Mello, the leader of the PqRMM/2 team, was finished in time to be presented during the Brazilian Independence Day Parade of September 7th 1973.

The first X1 ever built during the Independence Day Parade.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivative

The prototype was extensively tested, and accepted into service under the official designation of Viatura Blindada de Combate – Carro de Combate MB-1 (VBC CC Medio Bernardini-1). What is interesting about these is the MB-1 designation, which means Medium Bernardini-1. This suggests that Bernardini saw this as a medium tank, while the Army saw it as a light tank, which can also be seen on the side of the prototype, stating CL-X1: Carro Leve-X1 or Light Car/Tank X1.

The X1 prototype theory

It is unknown what happened with the X1 prototype afterwards. But after extensive research by studying the context and photographic evidence, the writer of this article proposes a new and very plausible theory to what happened with the X1 prototype and how it connects with the XLF-40.

It seems that the hull was repurposed for the XLF-40 project. Besides the X1, a bridge laying vehicle designated XLP-10 and a rocket launching vehicle designated XLF-40 were built. Both these variants would use the two hatch opening for the co-driver instead of a hull machine gun. What is interesting is that the XLP-10’s and all production X1’s used a single front side plate and the XLP-10’s missed a characteristic hook on the sides. The XLF-40, though, used the exact same double front side plates design as the X1 prototype and also offered the hook. Additionally, both the X1 prototype and the XLF-40 were converted from an M3A1 Stuart, identifiable from the rear. Considering the X1 prototype was trialled in 1974 and the XLF-40 was built in 1976, it is very likely that the Brazilians removed the production X1 turret to arm a production X1 and to subsequently repurpose the X1 prototype hull for the XLF-40 prototype. Just like the prototype turret, this makes perfect sense to not waste an otherwise perfectly fine hull and to cut costs in what was effectively a technology test bed.

A picture with the two plate front side plates encircled in red. This style was exclusive to the X1 prototype as all production vehicles used a single plate.
Source: http://www.gbnnews.com.br/2017/10/bernardini-um-historia-de-expertise-e.html#.YKLIoKHRZ1o & Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

With these arguments, the writer hopes to have sufficiently proved his theory that the X1 prototype hull was repurposed for the XLF-40. The writer would like to reinforce that this is still a theory and so far, only indirect and photographic images seem to point towards the possibility of this theory. No direct evidence was found to either confirm or deny this theory.

Production

With the acceptance of the prototype vehicle, a pre-series of 17 X1s was ordered in December 1973, which would be delivered to the 4th RCB in São Luiz Gonzaga, Rio Grande do Sul State. A series of setbacks would heavily delay the pre-series production, and it took 27 months, until February 1977, for all the pre-series vehicles to be built. The reasons for these delays were embargoes on certain components and issues with Bernardini. The company suffered from management problems, a lack of engineering knowledge, and felt it did not get enough credit. Also, by this time, the X1A1 and X1A2 projects, which were meant to replace the X1, were already in development.

Around this time, the X1’s would receive theri Army designations, the Carro de Combate Leve X1 Pioneiro (CCL X1 Pioneiro). The simple X1 and X1 Pioneiro designations would have been used more commonly. According to sources, it was manufactured under the designation CCL Biselli MB-1 Pioneiro, referring to both Biselli and Bernardini in its designation.

After the production of the pre-series, another batch of 17 vehicles was ordered for the 4th Regimentos de Cavalaria Blindados (RCB) (Englich: Armored Cavalry Regiment), and delivered on August 31st 1978, bringing the total number of X1s to 34 in the 4th RCB. During the same year, 17 other vehicles were delivered to the 6th RCB in Alegrete, Rio Grande do Sul State. Another X1 was delivered to the Academia Militar das Agulhas Negras (AMAN) (English: Black Needles Military Academy), a Brazilian West Point, and later transferred to the Escola de Material Bélico (EsMB) (English: School of Military Materiel). The total production run was 52 vehicles out of a possible 113 vehicles that were considered for production. By the time the X1 Pioneiros were delivered, the X1A2 entered production, which was in turn cancelled in favor of the M41C not long after, being developed from 1978 onwards. An interesting side note is that the X1s were built from both the M3 and M3A1 Stuarts. As a result, some X1s have flat rear plates (M3 Stuart), while others have curved rears (M3A1 Stuart).

X1s of the 4th RCB.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivative

The X1 Design

The length measurements turned out to be incorrect in the sources. As a result, all the length values were calculated and are reasonable estimates. The X1 weighed 17 tonnes (18.7 US tons) and was 6.04 meters (19.8 feet) long including the gun, had a 5.04 meters (16.4 feet) long hull, 2.4 meters (7.9 feet) wide, and 2.45 meters (8 feet) tall. It had a crew of four, with the driver located on the front left of the hull, the co-driver on the front right of the hull, the commander/loader on the left side of the turret, and the gunner on the right side of the turret.

X1s of the 6th RCB.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivative

Hull and Armor

The hull of the X1 was a lengthened and modified M3 or M3A1 Stuart hull. As such, the overall protection for most of the X1’s hull remained the same as that of the M3. The thickness of the plates which were used to lengthen the hull is unknown. The upper front plate of the X1 had an armor thickness of 38 mm (1.5 inch) at 17 degrees vertical, a middle front plate of 16 mm (0.6 inch) at 69 degrees, and a lower front plate of 44 mm (1.7 inch) at 23 degrees. Its sides were most likely about 25 mm (1 inch) thick. The rear armor and the lengthened parts of the side are unknown. Considering the original Stuart had 25 mm (1 inch) thickness on the sides and rear, it would not be unreasonable to assume that the lengthened structure was about 25 mm (1 inch) thick as well. The top plate would have been 13 mm (0.5 inch) thick and the floor plate would have gradually decreased in thickness from 13 mm at the front to 10 mm (0.5 to 0.4 inch) in the rear (although the thickness for the lengthened structure is unknown).

The rest of the X1 had a very similar layout as the Stuart. It had two headlights, one on each side of the front mudguards, two towing hooks on the front hull, and a .30 caliber hull machine gun on the right side. The driver had a two piece hatch, while the co-driver had a single piece hatch in the production versions of the X1. Depending on its variant, the X1 would either have a curved or angled rear plate, with the curved rear plate coming from the M3A1 Stuart.

X1 with a curved rear plate.
Source: https://wwiiafterwwii.files.wordpress.com/2020/09/x1preservedtanks.jpg?w=809

Mobility

The X1 was powered by a Scania-Vabis DS-11 A05 CC1 6-cylinder in-line diesel engine. This engine produced 256 hp at 2,200 rpm, giving the vehicle a horsepower per tonne ratio of 15.1. It used the same, but revised and partially nationalized, 5 speed and 1 reverse transmission and differential as the original Stuarts. The X1 had a top speed of 55 km/h (34 mph) on roads and an operational range of 520 kilometers (323 miles).

The X1 used a copied and slightly altered VVS suspension system from the 18-ton M4 artillery tractor. It had 4 road wheels divided over two bogies, with 2 bogies per track, two return rollers on each side, a drive sprocket in the front and an idler wheel on the rear. The 18-ton M4 suspension gave the X1 a ground pressure of 0.59 kg/cm2 (8.4 psi). The X1 had an on-ground track length of about 3.22 meters (10.6 foot) and could cross a trench of 1.2 meters (3.9 foot).

Turret

The production versions of the X1 used the BT-90A1 turret, which used periscopes from Vasconcelos S/A. This company had previously provided periscopes for the VBB-1 4 x 4 wheeled vehicle. The turret was armored with 25 mm (1 inch) thick steel plates at various angles to protect it from .50 caliber machine gun fire at 200 meters (218 yards). It is suggested that the overall turret layout and the internal turret construction and components were more or less copied from the French H-90 turret. It had the exact same turret ring and its overall shape seems to match the H-90. In addition, in the first BT-90 turret, a lot of equipment was carried over from the H-90, like the periscopes.

BT-90A1 rear interior.
Source: Caiafa Master – https://youtu.be/p1lUgv5eMsg

The BT-90A1 turret had a mount for a .50 machine gun on the left side of the turret, in front of the commander’s cupola. The commander’s cupola’s structure was slightly raised from the turret top to provide the commander with a 360 degree view. The antenna of the radio sets was located behind the gunner’s cupola on the right side of the turret. In addition, the X1 could mount two smoke dischargers on both sides of the turret rear, although these seem to not have always been mounted on the vehicles.

BT-90A1 rear interior.
Source: Caiafa Master – https://youtu.be/p1lUgv5eMsg

Armament

The X1 was armed with the 90 mm D-921 low-pressure gun. The low-pressure gun allowed vehicles like the X1, but also the 5 tonne AML-90 to mount a gun with significant armor penetration capabilities.

The trade-off with these types of guns is that Kinetic Armor Piercing (AP) or Armor Piercing Fin-Stabilized Discarding Sabot (APFSDS) rounds are not really worth it from a penetration point of view compared to the High Explosive Anti Tank (HEAT) rounds. A 90 mm APFSDS round for the later Cockerill guns would penetrate 100 mm (3.9 inch) of armor at 60 degrees from vertical at a range of 1,000 meters (1,090 yards), compared to 130 mm (5.1 inch) at 60 degrees for HEAT at any range. The D-921 did not even have AP rounds available for this reason.

The 90 mm D-921 gun.
Source: https://forum.warthunder.com/index.php?/topic/393523-panhard-aml-90-linx/

The X1 had access to HEAT and High Explosive rounds. The HEAT round was meant for anti-armor purposes and was the X1’s anti-tank round. The HE round was used as a general purpose support round. Another downside with these low-pressure guns was their limited combat range and decreased velocity. This meant that the gun became much less accurate at longer ranges compared to high velocity guns, which could also outrange the low-pressure 90 mm guns.

Round

Capability

Effective range

Velocity

HEAT (High Explosive Anti Tank)

130 mm at 60 degrees from vertical or 350 mm flat at any range.

1,500 meters (1,640 yards)

865 m/s

HE (High Explosive)

Lethal radius of 15 meters (16 yards)

700 m/s

The X1 stowed 18 rounds in the turret, and an additional 10 rounds in the hull, for a total of 28 rounds of 90 mm ammunition. In addition to the 90 mm, the X1 mounted a turret top .50 caliber machine gun for the commander, a coaciel .30 machine gun, and a .30 machine gun for the co-driver in the hull.

The very first X1 during firing trials in 1974.
Source: Blindados no Brasil

The X1 Family

The X1 was meant to become a family of vehicles for the Brazilian Army and, later, a potential export vehicle/conversion possibility for Bernardini. As such, the X1 has spawned many variants or vehicles which are part of its family.

X1A1

The X1A1 was supposed to be the improved version of the X1, which would fix a few of the X1’s initial shortcomings. It was further lengthened and the turret was enlarged as well. The transmission was replaced along with the brakes. Although the X1A1 meant to fix some mobility issues, it brought a new mobility issue forward. The lengthening caused the track length to vehicle width ratio to be too large, causing the X1A1 to be difficult to steer. To fix these issues, extensive measures would have had to be undertaken. Designing their own hull, in the shape of the X1A2, was relatively easier and more effective. Only one X1A1 was built, and Biselli left the X1 family project somewhere around this time.

X1A1 on the left, next to an X1. Note the additional bogie and the lengthened turret.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

X1A2

The X1A2 was the first, and up to now (2021), the only serially produced tank fully designed and mostly built in Brazil which was used in active service. The X1A2 was, in contrast to the rest of the X1 family, not built with a Stuart hull as basis, but featured a completely new design. In addition, the X1A2 was armed with an EC-90 low-pressure gun like the later EE-9 Cascavels. 24 X1A2s were built before the program was cancelled in favor of modernizing the M41 Walker Bulldog.

X1A2
Source: Image Caiafa

XLP-10

One of the planned vehicles for the X1 family was a bridge laying vehicle. Both the CPDB and the IME would design their own style of bridge laying mechanism, of which the hydraulic design from CPDB won. The bridge was 10 meter long, but it was only fit for the X1 family, which meant that the M41 could not cross the bridge. Five bridge laying vehicles were built, of which none remain.

XLP-10
Source: https://www.cibld.eb.mil.br/index.php/historico-2/blindados-eb-parte-3

XLF-40

Research on rockets started in the 1950s and, eventually, the ETE, IME, and Avibras developed the X-40 rocket. The rockets showed great potential and, as a result, in late June 1976, the XLF-40 project started its development. The only prototype was completed 2 months later. The XLF-40 project was of great importance for the company Avibras, as they gained more experience in the development of rocket systems, which would result in the ASTROS II missile system. The 40 stands for the X-40 rockets used by the vehicle.

XLF-40
Source: https://www.cibld.eb.mil.br/index.php/historico-2/blindados-eb-parte-3

XM3B1

This was a mortar carrier version of the X1, designed to resemble an M113. It mounted a 120 mm M957 mortar operated by three servicemen and a driver. The vehicle was too small to carry its own ammunition, and the force of the mortar’s blast caused the side plates of the vehicle to start bending. Only 1 vehicle seems to have been made.

The XM3B1.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

XM3C1

The XM3C1 was a recovery vehicle similar in design and appearance to the mortar carrier XM3B1, but heavier. However, its role was more akin to an engineering vehicle. It had a Munck type winch and a draw bar to haul AFV’s and remove engines. It was armed with a .50 cal. As far as it is known, only a single of these vehicles was built.

XM3C1 on the left and the XM3B1 on the right.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

XM3D1

The XM3D1 was a revival of an earlier project based on the M3 Stuart, arming an X1 hull with an M55 Maxson quad .50 caliber machine gun turret. The Maxson mount was copied by a Brazilian company and would be used for Anti-Aircraft (AA) purposes, and could mount 2 20 mm cannons as well. As far as it is known, only one vehicle was ever built. The XM3D1 found its unfortunate fate on the wrong side of a B1 Centauro barrel, as it was used as a range target when the B1 was trialed in 2001.

The XM3D1, note the angled rear plate.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

XM3E1

This was another continuation of a previous project on the M3 Stuart for AA purposes. It comprised the installation of a Bofors 40 mm L60 gun within a turret on the X1 hull. Work was initiated, and the vehicle would have a considerably lower hull than the other X1s. Because of the lowered hull, the turret had to be placed on the left side of the hull to make room for the drive shaft. Eventually the project was cancelled before the Bofors was ever mounted, and it would receive the same Maxson turret as the XM3D1. It would later be used as a towing vehicle and the Maxson turret was removed. The XM3E1 still exists at the Museu Militar Conde de Linhares.

The XM3E1 hull.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

X1P

The X1P was an overhaul of Paraguayan Stuarts which were previously gifted by Brazil. This overhaul was done for free as a sign of goodwill by Brazil and was carried out by Bernardini and the CTEx. Brazil and Bernardini hoped that this overhaul would sway the Paraguayan Army to buy the X1A2. This never happened and Paraguay would continue operating the now overhauled Stuarts. The X1P had a general maintenance overhaul and received the Scania-Vabis engine, like the X1.

The X1P.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

X-MAR

The X-MAR was part of a project from the CFN and Biselli to develop a series of vehicles for the CFN in the mid-1970s. Among these projects was a project for a tracked armored fighting vehicle, which would become the X-MAR. The X-MAR was supposed to receive a copied M41 Walker Bulldog style suspension from Dacunha Veículos e Mecânica S/A. Due to internal issues in Biselli, the projects would be cancelled, and the planned vehicles for the CFN would not come to be. Although Dacunha would try until 1980 to mount their copied M41 suspension on a Stuart, the Army would not give them a vehicle to do so.

The X-MAR sketch.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

X1 60 mm HVMS

During the 1980s, Bernardini was in negotiations with the Ecuadorian Army to convert their M3A1 Stuarts. The Stuarts would receive the 60 mm HVMS gun, which was used by the Chileans on their M50 Sherman and their M24 Chaffee. In addition, the Stuarts would be powered with a Detroit 6V53T diesel engine. Due to directive changes within the Ecuadorian Armed Forces, the project would be cancelled (potentially due to the acquisition of the EE-9 Cascavel).

X1 Bulldozer, Mine Clearing, and Ambulance

These three types of X1s were only studied and never left the drawing board, if they were actually drawn in the first place. Nothing is known about these vehicles except that they were studied for a brief while, but would never be built or further developed.

Service

Considering Brazil never went to war after World War 2, and its main issues were dealing with guerillas, the armored vehicles of Brazil have a practically non-existent combat service within the Brazilian Army.

In between 1977 and 1978, a total of 34 X1s would be delivered to the 4th RCB in São Luiz Gonzaga, Rio Grande do Sul State. The 34 vehicles equipped 2 squadrons, consisting of 17 vehicles each, and would serve for four years alongside the VBTP Urutu, until the M113 would take over this role in 1982.

The X1 and an M113 of the 4th RCB.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

In 1978, 17 X1s were delivered to the 6th RCB in Alegrete, Rio Grande do Sul State. There, it filled a single squadron, replacing the M4 Sherman squadron. It served with the Urutu as well, which would also be replaced with M113s in 1987. In addition, the 6th RCB was the only squadron to receive the X1A2, operating 10 vehicles and replacing the second squadron of M4 Shermans in 1981.

The X1A2 on the left and the X1 on the right during live-fire practice of the 6th RCB.
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives

Throughout its service life, the X1 would show a number of issues. Most of these could be blamed on the age of the Stuart, considering the 6th RCB, which had received X1s which were converted from better quality Stuarts, had much fewer issues than the 4th RCB. Among these issues were a flawed single disc clutch, locally produced volute springs that broke and would later be replaced by imported springs, and the swing arms of the track idler starting to crack when the X1 moved at full speed.

This last issue seems to have been the most severe, as the system was apparently unable to take the weight of the X1 in combination with its speed and cross-country operations. The first instance of the swing arms cracking was in December 1979 on an X1 of the 4th RCB, after 1,570 hours of operations. This problem would also appear on X1s with as little as 200 hours of operational service. By February 1983, 8 X1s of the 4th RCB were out of operation because of this issue. By the end of 1983, only 2 of the 34 X1 vehicles of the 4th RCB would be operational.

Eventually, the problem which caused the cracking was found: the copied 18-ton suspension used a grease cup instead of oil lubrication for the bearing of the idler. Since grease has a higher viscosity than oil, it was unable to properly flow and lubricate the bearing, causing the idler wheels to get stuck and subsequently tear the swing arms apart. In June 1984, this issue was resolved by returning to oil lubrication, and the 4th RCB would operate 23 X1s after repair works were carried out. Initially, it was planned for Bernardini to produce 58 new idlers, but the costs were so high that this was abandoned.

In addition to the swing arms cracking, the hull also started to crack at the mounting point of the bogies. This was caused due to improper supporting of the bogie suspensions with the increased weight of the vehicles. Biselli seemed to not have fully committed to the X1 project at the time, which might have caused them to improperly design the mounting. It has to be noted that there was also a lack of operational and maintenance manuals, which most likely caused the vehicles to deteriorate faster than they should have.

The X1 would be gradually replaced by the M41C in 1988, and would be decommissioned in July 1994. It is suggested that some X1s were used as training vehicles, as they were cheaper than the M41C.

The M41C.
Source: http://www.lexicarbrasil.com.br

Fate

The X1s would be gradually phased out by the M41s. Most X1s seem to have been scraped, but a decent amount can still be found at multiple locations in Brazil. Various X1s ended up as gate guardians for military bases and institutions, and they are also presented in the Museu Militar Conde de Linhares alongside some variants of the X1. The X1 was never really a very good tank, with the Commander of the AMAN stating that the X1 compromises the fighting power of Brazil, and that it was more of a useful tool to get to the height of their commitments: an adequate national tank. This is really what the X1 project was. They were not particularly good vehicles, but more of a stopgap and a project to gain the experience to eventually build the vehicles that fitted with Brazil’s wishes.

Conclusion

The X1 was a more or less successful attempt by the Brazilian Army and its rising defense industry to convert an obsolete tank into a service-worthy vehicle. The X1 was the apex of the M3 Stuart, considering the X1A1 was a failure and the X1A2 was not converted from a Stuart. Brazil managed to create an extensive family of vehicles to support the X1 and all its variants for potential combat service, but only a few would ever see service, become a prototype or see the light of day.

The eventual development of the X1 might be a bit questionable, considering Engesa’s EE-9 Cascavel was, for all intents and purposes, an equal if not better vehicle. But this does not take away from the actual goal of the Brazilian defense industry at the time, which was not to create an exceptional combat vehicle. The X1 was developed and built to gain experience in the manufacture and conversion of armored vehicles, which would later be carried out on more complicated vehicles, like the M41 Walker Bulldog. The X1 just needed to extend the service life and improve the combat effectiveness of the M3 Stuart until the M41C project could be initiated. The low weight of the X1 was seen as an extra advantage, considering the infrastructure and terrain on which the Brazilian Army might have had to fight, which would have been much harder with heavier vehicles.

Nevertheless, the X1 did have some significant issues, which took some years to address. As such, the X1 can be seen as an inadequate vehicle service wise, considering that more than half of the X1 fleet was out of operation for a year until 1984, because of a problem that was first found in 1979. The X1 can be summarized as a vehicle which achieved its eventual goal from the bigger defense industry picture, but did not perform or was not necessarily much more useful than other equipment which the Brazilian Army had in service.

Illustrations

X1 converted from an M3 Stuart. Done by Brian Gaydos.
X1 converted from an M3A1 Stuart. Done by Brian Gaydos.

Specifications CCL X1

Dimensions (L-W-H) 6.04 meters (19.8 feet) long including the gun x 2.4 meters (7.9 feet) x 2.45 meters (8 feet) tall
Total weight 17 tonnes (18.7 US tons)
Crew 4 (Driver, Co-driver, Commander-Loader, Gunner)
Propulsion Scania-Vabis DS-11 A05 CC1 6-cylinder in-line 256 hp diesel engine
Suspension Bogie suspension
Speed (road) 55 kph (34 mph)
Operational range 520 km (323 miles)
Armament 90 mm D-921 low-pressure gun
.50 machine gun
.30 coaxial machine gun
.30 hull machine gun
Armor

Hull

Front (Upper Glacis) 38 mm (1.5 inch) at 17 degrees
Front (Middle Glacis) 16 mm (0.6 inch) at 69 degrees
Front (Lower Glacis) 44 mm (1.7 inch) at 23 degrees
Sides (guess) 25 mm (1 inch)
Rear (guess) 25 mm (1 inch)
Top 13 mm (0.5 inch)
Floor 13 to 10 mm (0.5 to 0.4 inch)

Turret

25 mm (1 inch) allround

Production 52 + 1 Prototype

Special thanks to Expedito Carlos Stephani Bastos, the leading expert in Brazilian vehicles, please visit his website for further reading on Brazilian vehicles: https://ecsbdefesa.com.br/, Jose Antonio Valls, an Ex-Engesa employee and expert in Engesa vehicles, Paulo Bastos, another leading expert of Brazilian Armored vehicles and the author of the book on Brazilian Stuarts and the website https://tecnodefesa.com.br, Adriano Santiago Garcia, a Captain in the Brazilian Army and ex-company commander on the Leopard 1 and ex-lecturer on the Brazilian Armored School, and Guilherme Travassus Silva, a Brazilian with whom I was able to endlessly discuss Brazilian Vehicles and who was always willing to listen to my near endless ability to talk about them.

Dedicated to the Brazilian Army in celebration of a hundred years of tanks in Brazil

Sources

Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives – Hélio Higuchi, Paulo Roberto Bastos Jr., Reginaldo Bacchi
Blindados no Brasil – Expedito Carlos Stephani Bastos
Jane’s Light Tanks and Armoured Cars of 1984
Worldwide Tank Fire-Control Systems – CIA
http://www.lexicarbrasil.com.br/
Personal correspondence with Expedito Carlos Stephani Bastos
Personal correspondence with Paulo Roberto Bastos Jr.
Caiafa Master
Engesa brochures and manuals
Cockerill brochures
TM 9-785 18-Ton High Speed Tractors M4, M4A1, M4C, and M4A1C – US Army April 1952.
Stuart: A history of the American Light Tank, Volume 1 – R.P. Hunnicutt
Tecnologia Militar Brasileira magazine

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