The EE-T1 Osorio was considered for service with the Saudi Arabian Army. It was evaluated against the French AMX 40, the American M1 Abrams, and the British Challenger 1, and emerged as the winner. In September 1989, Saudi Arabia quietly opted for the M1 Abrams instead and only announced its new decision shortly after Iraq invaded neighboring Kuwait, triggering the Persian Gulf War. The two prototypes were given to the Brazilian Army as result of Engesa going bankrupt.
That being the situation, Engesa decided to go on with the project by itself, a decision that would prove later to be too risky. In face of the way the Brazilian state participated in the Brazilian armament industry at that time, some restrictions imposed by the Brazilian Army had to be considered. The first one stated that the new MBT should weigh no more than 36 tons, which was a technical impossibility, as it would set the Brazilian MBT outside of the first class MBT's weight, which was between 44.5 tons (T-72) and 62 tons (Challenger), at that time. The second Brazilian Army's restriction was that the maximum width of the new MBT could not be larger that 3.20 meters, a limit imposed by the Brazilian railway structure.
The first turret, the "default", was designed to accommodate the British 105mm L7 series gun, which was NATO's main battle tank gun specification, until the 120 mm L/44 Rheinmetall gun was adopted, but at that time, this was still to happen in the future. The British 105 mm L7 series gun was an excellent option, because it was used by so many countries, its cost was reasonable, and there were many types of ammunition available for its use. The fire control system for this turret, fully computerized, consisted of a laser range finder and a LRS-5DNLC Olp Belgian periscope, and the commander had an LRS-5DN periscope. This fire control system and the main gun were fully stabilized.
The second turret was developed for being used by the Saudi Arabia's Army. This turret would receive the French smooth-bore 120mm GIAT G1 gun, because tests proved that the British rifled 120mm L11 gun, although more powerful, also had stronger recoil forces, that a 42 ton MBT could not support. The German Rheinmetall 120 mm L/44 smooth-bore gun was not tested because of the weapons selling politics of the German government at that time.