Cold War Brazilian Armor Cold War Ecuadorian Armor

CCL X1 with 60 HVMS Brazil/Ecuador (1980s)
Light Tank – None Built

At some point in the 1980s, Ecuador sought to upgrade its fleet of M3A1 Stuarts by modernizing them with a new gun and engine. The country entered negotiations with the Brazilian company Bernardini, which in the mid-1970s had modernized the Brazilian M3 Stuart to X1 standard. The negotiations considered a refurbished M3A1 Stuart armed with a 60 mm HVMS gun, which also armed the Chilean M4 Sherman and M24 Chaffee, and a Detroit 6V53T engine. Although the project would never leave the concept stage, the X1 60 HVMS would have had the best anti-tank capabilities of the entire X1 family. Sadly, a limited budget and an order of 32 EE-9 Cascavels by the Ecuadorian Army seem to have put an end to the project.

An Illustration of what the X1 armed with the 60 mm HVMS might have looked like. Done by David Bocquelet, edited by Brian Gaydos.

The M3A1 Stuart in Ecuador

Ecuador received the M3A1 Stuart under Lend-Lease from the United States. With World War 2 in full swing and the United States at war with the Axis, the United States sought to secure its position on the American continent. Through multiple ways, the United States would successfully influence all the American countries to either side with the Allies or stay neutral throughout the conflict. Ecuador remained neutral for the majority of World War 2, only declaring war on Germany and Japan on February 2nd, 1945.

In their attempt to secure the American continent, the United States realized that most of the equipment of the armies and infrastructure of the American countries were seriously outdated. Thus, Ecuador would receive military materiel from the United States to modernize the country’s Armed Forces for the safety of the American continent, but also as a deterrent for any country on the continent itself to join the war on the Axis side.

Ecuador received M3A1 Stuarts, M3 Scout Cars, and machine guns through Lend-Lease. In exchange, the United States could use the Galapagos Islands (off the coast of Ecuador, in the Pacific) as a base during World War 2. Ecuador received 42 M3A1 Stuarts, which arrived in 1943, after the Ecuadorian-Peruvian War of 1941. Supposedly, the M3 Stuarts were delivered to Ecuador in a non-combat ready state. If this meant that the Americans had not delivered the ammunition with the tanks or if the Americans had done something else to make them non-combat ready is unknown. The reason for the United States to supposedly deliver them in this state was to prevent a revenge attack by the Ecuadorians on Peru after their defeat during the Ecuador-Peruvian War. It is unclear how far these statements on combat readiness are true, so it is wise to take them with a grain of salt.

M3A1 Stuarts in the Ecuadorian Highlands.

The X1

The first X1 vehicle was developed and presented at the Brazilian Independence Day Parade on September 7th 1973. The X1 was a modernization project of the M3 Stuart, carried out by the Parque Regional de Motomecanização da 2a Região Militar (PqRMM/2) (English: Regional Motomecanization Park of the 2nd Military Region), alongside Bernardini and Biselli, two Brazilian companies. The PqRMM/2 was responsible for the development of the wheeled vehicles, but also for the tracked vehicles of the Brazilian Army at the time, and were under the supervision of the Diretoria de Pesquisa e Ensino Técnico (DPET) (English: Army Research and Technical Educational Board), which coordinated the projects.

The tracked vehicles were researched and developed by a team of engineers within the Army and PqRMM/2, which were part of the Centro de Pesquisa e Desenvolvimento de Blindados (CPDB) (English: Centre for the Research and Development of Tanks). The CPDB was a research group of Army engineers which analyzed 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.

A Brazilian M3 Stuart approved for conversion, note the A on the side meaning Aprovado (English: Approved).
Source: Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivative

The reasons for the M3 Stuart modernization were the lack of new and cheap materiel from the United States (then involved in the Vietnam War), the fact that they were the most numerous vehicles to be converted, that they were cheap to run and maintain, and their lightweight made them perfect for fighting on the difficult terrains of Brazil and their neighboring countries if needed. But the most important reason was that they were relatively easy and low risk to convert in order to gain experience to eventually build a national Brazilian tank. The M41s which Brazil had at the time were their best vehicles and much more risky to improve with the lack of experience.

After having successfully developed the first X1, a pre-series of 17 vehicles was ordered. These vehicles would, due to extensive delays, finally be delivered in 1976. The X1 was armed with a 90 mm D-921 low-pressure gun and had a Scania-Vabis DS-11 A05 CC1 6-cylinder in-line 256 hp diesel engine.

The X1.
Source: Blindados no Brasil

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 Cash-in-Transit 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. Biselli quit the X1 project altogether around 1976, leaving the X1 family fully in the hands of Bernardini. In 1982, Bernardini was contracted by the Brazilian Army to develop a family of vehicles on the M3 Stuart and X1 platform. This contract would result in a family of vehicles, for example, a recovery version and a mortar carrier.

It is important to note that since Biselli quit the X1 project entirely around 1976, they had nothing to do with the X1 60 HVMS project for Ecuador. In fact, every development of the X1 family undertaken after 1976 was done by Bernardini, and the intellectual property of the vehicle was completely signed off to Bernardini by the Army.



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

An X1 for Ecuador?

Very little is known about the X1 60 HVMS for Ecuador. According to sources, the negotiations for the conversion of an unknown amount of Ecuadorian M3A1 Stuarts were carried out at some point in the 1980s. In total, Ecuador had received 42 M3A1 Stuarts, but it is unlikely that all 42 vehicles were still in service, or even fit for refurbishment at all. It is estimated that Ecuador might have been interested in the conversion of around 30 M3A1 Stuarts. This estimation is based on an order of 32 EE-9 Cascavels which might have been ordered instead of the X1 60 HVMS.

EE-9 Cascavel.

The Ecuadorian Army asked for the refurbishment of their existing M3A1 Stuart, rearming them with the 60 mm HVMS, and remotorizing them with a Detroit 6V53T diesel engine. It is thought that the vehicle would effectively be an X1 with changes to the turret to mount the 60 mm cannon and a new engine.

It is estimated that the negotiations between Ecuador and Bernardini started at some point between 1980 and 1984, and most likely from 1982 to 1983. The reason for this is that negotiations were done in the 1980s, and Bernardini received the intellectual property and the contract to develop a family of X1 vehicles in 1982. Considering the X1 60 HVMS never got much further than the concept stage, it is very likely that the negotiations were short and might even only have happened for about a year. The reason given for the cancellation of the project was due to changes at the top of the Ecuadorian Army.

A few factors can be taken into account which might have led to the cancellation of the X1 60 HVMS project and why it is thought that the project was canceled in 1983. From 1977 to 1984, Ecuador was cutting the Army’s budget every year, reaching its lowest point in 1984. The budget of the Ecuadorian Army was somewhat limited for the acquisition of armored vehicles. In addition, 32 EE-9 Cascavels, armed with 90 mm low-pressure guns, were bought from Engesa in 1983 and delivered in 1984. It is very likely that the EE-9 Cascavel order sucked up the budget of the Ecuadorian Army, and combined with another budget cut in 1984, the Army simply did not have the money to spend on the conversion of their M3A1 Stuart tank fleet.

In addition, another case can be made for the EE-9 against the X1. The EE-9 was a brand new vehicle, while the X1 would be converted from 40-year-old vehicles. As shown by the X1 conversion in Brazil, certain issues cannot simply be fixed due to the sheer age of the refurbished vehicle. It begs the question, why spend money upgrading something old which will still retain unsolvable issues, when one could buy brand new armored cars?

An Ecuadorian M3A1 Stuart in a military parade in 2018.

The 60 HVMS gun

The 60 mm Hyper Velocity Medium Support L.70 gun was developed in 1977 by the Israeli Military Industry and the Italian company OTO-Melara to provide the infantry with a towed or Infantry Fighting Vehicle-mounted gun that could provide excellent anti-tank fire and adequate anti-infantry support. It was tested by Israel on a modified M113 with a turret and by the Italians on the VBM Freccia prototype and on a modified VCC-80 Dardo, but was not accepted into service.

The 60 HVMS on a carriage during shooting tests.

In fact, the 60 HVMS IMI-OTO (known in Italy as the HVMS 60/70 OTO-Melara) had excellent anti-tank performance and was able to penetrate, with its M300 APDSFS-T (Armor-Piercing Fin-Stabilized Discarding Sabot – Tracer), 120 mm of Rolled Homogeneous Armor (RHA) angled at 60° at a 2,000 m range. This was the equivalent of the frontal armor of a Soviet T-62.
In one test, it allegedly managed to penetrate the side armor of two T-62s from side to side at 2,000 m. As an example, a 105 mm APDSFS-T projectile from the Royal Ordnance L7 penetrated the same armor at the same distance. However, the 60 mm gun weighed 700 kg with a total projectile weight of only 6 kg and a length of 62 cm, while the Royal Ordnance L7 weighed 1,200 kg with projectiles weighing around 18 kg and a length of about 95 cm.

The tungsten penetrator of the APDSFS-T projectile weighed 0.87 kg with a diameter of 17 mm and a total length of 292 mm. It had a muzzle velocity of 1,620 m/s thanks to the high-pressure barrel, giving it very good accuracy up to a 2,500 m range. The HE-T (High-Explosive – Tracer) projectile weighed 7.2 kg.

A Spanish language OTO-Melara poster on the APFSDS and HE rounds of the 60 HVMS guns.
Source: Foro Militar Genera

The Theoretical X1 60 HVMS Design in Detail

The specifications and design of the X1 60 HVMS are mainly based on the existing specifications of the X1, with adjustments for the 60 HVMS gun and the Detroit 6V53T engine, to give an idea of what a 60 HVMS armed X1 might have been.

The length measurements of the X1 turned out to be incorrect in the sources. As a result, all the length values were calculated and are reasonable estimates. The X1 60 HVMS would have weighed about 17 tonnes (18.7 US tons) and would be 7.24 meters (23.7 feet) long including the gun, compared with the 6.04 meters (19.8 feet) of the normal X1, with a 5.04 meters (16.4 feet) long hull, 2.4 meters (7.9 feet) width, and 2.45 meters (8 feet) high. Although the 60 HVMS was about 300 kg heavier than the original 90 mm D-921, the difference in weight would be compensated by the Detroit engine, which was about 300 kg lighter than the original Scania engine.

It would have 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.

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

Hull and Armor

The hull of the X1 HVMS was to be a lengthened and modified M3A1 Stuart hull. As such, the overall protection for most of the X1 HVMS’ hull remained the same as that of the M3A1. The thickness of the plates which were used to lengthen the hull is unknown. The upper front plate of the X1 HVMS would have an armor thickness of 38 mm (1.5 inch) at 17º vertical, a middle front plate of 16 mm (0.6 inch) at 69º, and a lower front plate of 44 mm (1.7 inch) at 23º. 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 HVMS would have a very similar layout as the Stuart, like the original X1. The X1 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.

Brazilian X1 with a curved rear plate.


The X1 HVMS was to be powered by a Detroit 6V53T V6 turbocharged 260 hp diesel engine. This engine produced 260 hp at 2,200 rpm, giving the vehicle a horsepower per tonne ratio of 15.3. It would have used the same, but revised and using some locally produced components, 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 HVMS would have 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 HVMS 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 feet) and could cross a trench of 1.2 meters (3.9 feet).


It is thought that the X1 HVMS would most likely have kept the BT-90A1 turret of the X1, although adjusted for the 60 mm HVMS gun. Considering the HVMS has a recoil weight of 500 kg compared to 200 kg for the D-921, the trunion of the turret would have most likely needed reinforcement. The recoil length of the HMVS, however, was shorter at 270 mm compared to 550 for the 90 mm.

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, such as the periscopes.

BT-90A1 turret front interior.
Source: Caiafa Master –

The BT-90A1 turret had a mount for a .50 machine gun on the left side, 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 360º 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 –


The X1 60 HMVS was to be armed with the 60 mm HVMS gun. The HVMS gun would provide a couple of advantages over the 90 mm D-921 of the X1. Most notable was the heavily increased initial muzzle velocity of the APDSFS round for the HVMS gun of 1,620 m/s compared to 865 m/s for the HEAT round of the 90 mm gun of the X1. The APFSDS round would also retain its velocity much better due to better aerodynamic properties compared to the 90 mm round. The increased muzzle velocity combined with the small sub-caliber round would make the HVMS gun much more effective in the anti-tank role than the D-921 gun.

Since the D-921 gun fired its round with a much slower muzzle velocity, it became much less accurate as well. Not only did the gun need to fire the HEAT round at an angle to compensate for the lack of velocity, the gunner would also have to take the slower travel time into account while leading for a target. Overall, the longer the travel time of the round, the less accurate it gets.

Performance-wise, the HEAT round of the D-921 and the APFSDS round of the 60 mm HVMS were about equal in terms of penetration at 2,000 meters, at around 120 mm at 60º. However, the D-921 only had an effective range of 1,500 meters, meaning that the 60 mm HVMS would not only be more accurate, but also more effective at close ranges. All in all, the 60 mm HVMS was a much better anti-tank gun than the D-921, but compromised with a much lighter HE shell of 2.9 kg compared to 5.28 kg for the D-921.



Effective range


APFSDS-T (Armor-Piercing Fin-Stabilized Discarding Sabot – Tracer) 120 mm at 60 degrees from vertical at 2000 meters. 2,500 meters 1,620 m/s
HE (High Explosive)

It is unknown how many 60 mm rounds the X1 HVMS could have stored. The standard X1 stowed 18 rounds in the turret and another 10 in the hull. The X1 HVMS could probably have stored a little more. In addition to the 90 mm, the X1 mounted a turret top .50 caliber machine gun for the commander, a coaxial .30 machine gun, and a .30 machine gun for the co-driver in the hull.

An APFSDS round for the 60 mm gun.


Although the X1 60 HVMS was a very interesting project and would have greatly improved the anti-tank capability of the M3A1 Stuarts and the X1 family, it seems that the project lost to the EE-9 Cascavel. The basis of the X1 60 HVMS was 40 years old, which would make some issues unfixable due to the longevity of the platform. Combined with the decreasing budget of the Ecuadorian Army, the X1 60 HVMS was simply not meant to be. There was no money, the basis was too old, and the EE-9 was bought instead, dooming the project to obscurity.

An Ecuadorian EE-9 M7 Cascavel.


An Illustration of what the X1 armed with the 60 mm HVMS might have looked like. Done by David Bocquelet, edited by Brian Gaydos.

Specifications CCL X1

Dimensions (L-W-H) 7.24 meters (23.7 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 Detroit 6V53T V6 turbocharged 260 hp diesel engine
Suspension Bogie suspension
Speed (road) 55 kph (34 mph)
Operational range 520 km (323 miles)
Armament 60 mm HVMS gun
.50 machine gun
.30 coaxial machine gun
.30 hull machine gun


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)


25 mm (1 inch) allround

Production None (concept only)

Special thanks to Expedito Carlos Stephani Bastos, the leading expert in Brazilian vehicles, please visit his website for further reading on Brazilian vehicles:, 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, 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.


Brazilian Stuart – M3, M3A1, X1, X1A2 and their Derivatives – Hélio Higuchi, Paulo Roberto Bastos Jr., Reginaldo Bacchi
Blindados no Brasil – Expedito Carlos Stephani Bastos
Personal correspondence with Expedito Carlos Stephani Bastos
Personal correspondence with Paulo Roberto Bastos Jr.
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
Anuario – Academia de Historia Militar Number 33, 2019

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