The original M41 Walker Bulldog Light Tank was an American product of lessons learned through World War 2. Design work on the tank began in 1947 when it was known under its prototype name of "T37". Production of the series began in 1951 and, by the end of the Korean War (1950-1953), the M41 had completely supplanted the US Army's other light tank then in service - the World War 2-era M24 Chaffee. The M41 lived a healthy operational existence, was produced in the thousands and was fielded by over a dozen US-friendly nations around the world - including Brazil. The Brazilian Army operated some 300 "B" and "C" production series M41 Walker Bulldog light tanks beginning in 1953. During that span, several indigenous main battle tank projects came to light in an attempt to secure lucrative defense deals with the Brazilian government. Once such attempt became the Bernardini MB-3 "Tamoyo" Main Battle Tank which saw development in the 1980s - a product of Cold War experience.
In the early 1970s, the Brazilian concern of Bernardini S/A Industria e Comercio took on the role of modernizing the aging M41 fleet with the goal of the program intended to bring A and B series production models to a new government-stated "C" standard. While the program served to extend the battlefield usefulness of the original M41s to an extent, the Bernardini concern pushed for a greater reimagining of the original American design. In effect, the idea was to develop a Main Battle Tank out of the original light tank chassis as light tanks held little value on the modern battlefield of the Cold War - a battlefield where the MBT was now the undisputed king. The new ambitious MBT program was started in 1978 as Bernardini engineers worked to get the most out of the outdated M41 framework within reason and budget.
As such, the M41's turret and hull were completed reworked for the role. The hull now featured more angled facings to better deflect incoming enemy fire and artillery spray. The vehicle sat atop a suspended (torsion bar) wheeled system that included six road wheels to a track side. The glacis plate was well sloped from two plate sections at the front of the hull. The hull superstructure was shallow, offering a low side profile, and well-contoured from the glacis plate. The upper regions of the tracks were protected over with side "skirt" armor, these plates latching onto the hull sides. The engine compartment showcased a flat surface to compensate for the turret rear overhang. The turret itself was situated at the center of the hull roof and sported sloped sides with a flat top. There was a slightly raised commander's cupola with a machine gun pintle ahead of the position. The barrel was affixed to the front turret facing and overhung the front hull in conventional combat tank fashion. The new tank would be crewed by four personnel made up of the driver, gunner, commander and loader. Power was to be supplied by either a Saab-Scania DSI-14 diesel engine developing 500 horsepower or a Detroit Diesel 8V-92TA diesel engine of 730 horsepower depending on customer needs. This would have allowed for a maximum road speed of 67 to 70 kilometers per hour with an operational range of up to 550 kilometers. The powerplant was tied to either an Allison CD-500 Mechanic or General Electric HMPT-500 automatic transmission system. A crew NBC (Nuclear, Biological, Chemical) support system was optional. The vehicle could call upon 8x smoke grenades of a self-generated smoke screen effect.
A prototype form soon emerged in 1982 as the "X-30" and this model was completed with the rather limited M32 76mm main gun of the original the M41 Walker Bulldog. Nine more prototypes followed from 1983 through 1985 and these were given the more appropriate 90mm guns found in combat tanks elsewhere - though a move to the excellent L7A3 105mm caliber was already apparent globally. The 90mm guns were an in-house product engineered by Bernardini itself and some 68 x 90mm rounds could be stored aboard. It was only the 11th and final prototype that was given a heftier 105mm main gun system and this form appeared in 1987. Secondary armament would come in the form of a 7.62mm coaxial machine gun and a 12.7mm anti-aircraft machine gun - traditional defense weapons on any modern tank. Ammunition counts for the machine guns were 3,000 and 600 rounds respectively.
Evaluation of the prototypes continued for several years to which, at some point, the design also took on the name of MB-3 "Tamoyo". Brazilian authorities took an interest in its development but budget constraints were always an issue. Indigenous designs were always more expensive than procurement of "off the shelf" examples. To make matters worse, rival firm Engesa also put forth their EE-T1 "Osorio" MBT for contention around 1987 and this directly competed with the Bernardini design. Perhaps the final strike against both indigenous attempts came from the glut of used tanks available on the foreign market. This avenue proved the most fiscally sound and the Brazilians knew what they were getting with these machines. As such, authorities elected to purchase used German Leopard 1 and American M60A3 TTS (Tank Thermal Sight) MBTs in batches of 250 and 91 respectively, which forced Bernardini and Engesa to look elsewhere for potential buyers, doomed by forces beyond their control. Bernardini did not immediately give up its hopes to sell the Tamoyo to a foreign market but interest waned on the type. The Tamoyo was, therefore, never procured for serial production by any party - its legacy was secured by only the 11 completed prototypes.
There was also a proposed self-propelled anti-aircraft (SPAA) variant of the Tamoyo tank planned, this utilizing the tracked chassis and hull of the Tamoyo while the turret would have been replaced by a system mounting 2 x Bofors 40mm L/70 cannons. As a tracked system, the vehicle would roughly the same off-road capbilities of the parent Tamoyo.