EE-9 M4 APFSDS Testbed

Federative Republic of Brazil (1985)
Wheeled Reconnaissance Vehicle – 1 Built

In 1984, Engesa initiated the development of an APFSDS (Armor Piercing Fin Stabilized Discarding Sabot) round for the low pressure 90 mm gun of the EE-9. Why exactly Engesa entered such an endeavor is unknown, as kinetic energy projectiles are usually not viable for low pressure guns. Nevertheless, the round was developed and would offer a wider range of ammunition for their customers and make it look like the EE-9, now reaching 10 years of service, was still keeping up with modern developments of its time.

Developing an APFSDS round did not come without its challenges, however. Issues like the muzzle brake, a rifled barrel, materials and manufacturing processes had to be resolved. The culmination of the project seems to have taken place in July 1985, when an EE-9 fitted with a pepperpot-type muzzle brake was presented to an Iraqi delegation. This may suggest an Iraqi influence or interest in the APFSDS round, but sadly, the Iraqis did not end up acquiring the APFSDS round and the project was, for all intents and purposes, abandoned.

The EE-9 and Iraq

The story of why the EE-9 Cascavel (English: Rattlesnake) was developed can be traced back to the Second World War. Brazil sent an expeditionary force, known as the ‘Smoking Snakes’, to fight in Italy alongside the Allies. During the Italian campaign, the Brazilian forces were equipped with the 6-wheeled M8 Greyhound armored car. The Greyhound turned into a beloved vehicle for the Brazilian soldiers for its armor, simplicity and mobility, and after WW2, this love would remain embedded in the Brazilian Army.

Although Brazil enjoyed its diplomatic relations with the United States well into the 1970s, the first steps to break free from the United States, from an army materiel point of view, started in 1967. The United States had become increasingly involved with the Vietnam War and, as a result, could not supply Brazil with the cheap equipment it once did. As such, it was decided that the Brazilian Army would instead try to develop their own armored vehicles.

One of these was the EE-9 Cascavel, which was passed on to Engesa for production after the Army had developed a number of prototypes. The EE-9 was a 6 x 6 wheeled vehicle initially armed with a 37 mm, but would be armed with a 90 mm on suggestion of the Portuguese. While being the spiritual successor of the M8 Greyhound, two of the main innovations of the EE-9 were the usage of the boomerang suspension, which enabled it to cross much more difficult terrain ,and the incorporation of bimetallic armor, which offered improved protection over homogenous steel. Engesa managed to secure an export deal with Libya for 200 EE-9s in 1974 and, soon after, would receive an order for an additional 200 vehicles. From there, the EE-9 became Engesa’s flagship product, as they would sell it to multiple South American countries as well.

The use of the EE-9 Cascavel by Libya and its export success managed to get the attention of Iraq. After three weeks of negotiations, Engesa managed to secure the export contract for 364 EE-9s and 148 EE-11s on May 5th 1978. Iraq would be the first to receive a new model of EE-9, known as the EE-9 M4. In contrast to previous models, the EE-9 M4 used an MT-643 transmission which could handle the more powerful Detroit Diesel 6V53 212 hp engine. In addition, the hull featured a number of redesigns, like the integration of the headlights in the lower hull plate instead of the installation on top of the upper front plate. The most significant change was the redesigned ET-90 turret, known as ET-90 II, which was able to incorporate night vision sights.

A New Generation of Ammunition

Engesa was known for developing a wide range of concepts or options to market to potential customers. Some of these developments were fairly reasonable, while others just seem to have been developed for the sake of making a product and perhaps even the company looking more impressive. The EE-11 Urutu, effectively an EE-9 turned into an armored personnel carrier, was the prime subject for receiving all kinds of variants which tended to not generate any sales, but were extremely simple and cheap to manufacture nonetheless.

The development of the new EE-9 APFSDS (Armor Piercing Fin Stabilized Discarding Sabot) and canister (a round filled with steel balls) rounds may have been such a project according to an ex-Engesa employee, but could also have had some Iraqi influence as well. In 1984, the Engesa subsidiary Engequímica was founded, which was tasked with both the manufacture of all Engesa’s ammunition and the development of the new generation of EE-9 ammunition. The writer will refer to Engequímica for the development side of the ammunition while for the marketing and overarching business side the writer will refer to Engesa instead.

Considering the EE-9 was still very much the flagship product of Engesa, it is quite likely the company decided to make the gun seem more modern and appealing by offering an APFSDS round. While APFSDS was not a new concept, it had started to generate much more interest by the late 1970s, with NATO countries shifting from APDS (Armor Piercing Discarding Sabot) to APFSDS for both their 105 mm and 120 mm armament. The French also developed a wide range of APFSDS rounds for their high pressure 90 mm F4 guns, which would be mounted on the Brazilian Tamoyo 1 tank, and even some gun-mortars. At the time, Bernardini had also started to take steps by copying and subsequently manufacturing the French APFSDS round of the 90 mm F4 for the Tamoyo program.

Additionally, the Iraqi Army was thought to have requested the development of a canister round for the EE-9 Cascavel somewhere in 1984, as it was embroiled in the Iran-Iraq war at the time. At a similar time, General Amer Rashid had also requested the development of an anti-air EE-9 and it could be that he requested the development of the new ammunition as well. Why exactly the Iraqis sought a canister round for the EE-9 is unknown. It was likely that the canister round was requested to make the EE-9 better equipped against dealing with infantry formations. The Engequímica team developing the round called it the Cartucheira Gigante or Giant Cartridge in English. When the round was fired, it could sweep everything in a cone of about 20 meters (22 yards) wide at a distance 100 meters (109 yards) away, basically functioning like a giant shotgun. In the end, both the APFSDS and canister rounds were presented to an Iraqi delegation.

The canister round weighed 6.2 kg in total and was filled with 1,400 steel balls. Each ball had a diameter of 6 mm (0.25 inch) and weighed 0.88 grams for a total of 1.23 kg of balls inside the round. The effective range of the round was said to have been 150 to 200 meters (164 to 219 yards) and the muzzle velocity was around 520 m/s. Interestingly, Iraq supposedly also requested for the development of a longer range shrapnel round, which seems to appear in an Engesa brochure. Here, the shrapnel round had a muzzle velocity of 600 m/s and an effective range of 700 meters (765 yards). The maximum range was 800 meters (875 yards) with a dispersion of 1 mil (1 meter at 1,000 meters). In contrast to the canister round, which would function like a shotgun, the shrapnel round would detonate at a certain range and act like a large grenade.

The EC-90 Gun

Initially in 1974, Engesa sold the EE-9 Cascavel with the H-90 turret and the 90 mm D921 gun from the French, which was initially used on the AML-90. While preferring to only acquire the guns, the French only sold the gun and turret in a single package. As such, Bolivia, Chile and Libya received the French package. This was fairly advantageous for Engesa, as the AML-90 was widely available to their customer base and crews would need little retraining to serve in an EE-9.

As 284 EE-9s with the French turret were sold, the French caught on to the competitive challenge the vehicle could have on their own export market. As a result, the French raised the turret prices to such an amount that Engesa had no choice but to look for a different option. They found their solution with the Belgian company Cockerill and the EC-90 gun.

The EC-90 90 mm gun was a license production from the Cockerill Mk.3. Engesa acquired the license to produce the low-pressure 90 mm Cockerill 90 Mk. 3 gun in 1975 for US$3 million (US$15.5 million in 2021). The gun would be designated EC-90 by Engesa, with the E standing for Engesa, C for Canhão (Cannon), and 90 for the 90 mm gun. This license deal not only made it possible for Engesa to manufacture their own guns, but it also opened the door for them to design their own turrets. Additionally, due to the incorporation of the bimetallic steel armor, these turrets were also better protected than the French counterparts.

Low Pressure APFSDS?

Developing an APFSDS round for the EC-90 gun did come with a number of issues -the biggest being the very nature of the gun. The EC-90 was a so-called low pressure gun. This meant that the gun used low muzzle velocities which allowed larger caliber guns to be installed on extremely light platforms, such as the 5.5 tonne AML-90 or even a Toyota Technical. The use of low muzzle velocities entailed that traditional kinetic energy (K.E.) based anti-tank rounds, like AP and APDS, became unfeasible, as they relied on high muzzle velocities and thus high pressures for penetration performance.

This issue was circumvented by the usage of chemical energy (C.E.) ammunition, known as HEAT (High Explosive anti-Tank) and HESH (High Explosive Squash Head) ammunition. Chemical energy ammunition takes its penetration performance from the chemical charges inside the ammunition. As such, chemical energy ammunition performance was mostly bound by gun diameter rather than muzzle velocity. This meant that a HEAT round would have the same penetration at point blank as at 1,000 meters (1094 yards), as the potential penetration energy stored inside the round remained the same. Higher muzzle velocities mainly had influence on the accuracy and maximum effective range of the HEAT rounds.

This made low velocity 90 mm guns extremely dangerous, as the HEAT round of the French D921 could penetrate around 320 mm (12.6 inches) of flat steel armor at any range, while the Cockerill and EC-90 could penetrate around 250 mm (10 inches) of flat steel armor at any range as well. The difference in performance had to do with the French expertise in the development of HEAT ammunition. In just a few years, light reconnaissance platforms which previously were lightly armed and posed little threat to main battle tanks could theoretically destroy tanks like the T-55 family and the M48 Patton, even when engaging them frontally.

With the introduction of APFSDS, this performance gap between kinetic and chemical energy ammunition on low pressure guns became more equal. As APFSDS did not require spin stabilization, both the Length to Diameter ratio (L/D ratio), and velocity could be increased, boosting penetration performance. This change over the older AP and APDS rounds made the use of a kinetic energy round in the form of APFSDS more practical from low pressure guns.

The APFSDS round would still be somewhat inferior in penetration performance compared to a HEAT round for the 90 mm low pressure guns, but the gap was closed. The APFSDS round which was developed on the EE-9 was rated to penetrate a NATO single medium plate at 1,100 meters (1,200 yards), or 130 mm (5.1 inches) at 60° at 1,100 meters. Interestingly however, a later APFSDS round from Cockerill with fairly similar specifications is only rated in Cockerill’s brochures as 100 mm (4 inches) at 60° at 1,000 meters. Although there is variation as to exactly how these tests were conducted, it seems logical to assume that the APFSDS round of Engesa penetrated anywhere from 100 to 130 mm at 60° at 1,000 meters. Comparatively, this is marginally worse than the HEAT round, which is rated at 130 mm at 60° at any range.

It is also interesting to note that Engesa marketed the APFSDS round not as being a better round than the HEAT round in penetration performance, but in terms of the hit probability. The APFSDS boasted a higher but still relatively low muzzle velocity of 1,175 m/s, compared to the 890 m/s of the HEAT ammunition. However, the velocity increase and the much smaller projectile meant that accuracy of the APFSDS round at 1,000 meters was doubled from 0.8 mils (0.8 meters at 1,000 meters) dispersion of the HEAT round to 0.4 mils (0.4 meters at 1,000 meters). Additionally, the effective range doubled as well from 1,000 m to 2,000 m and the maximum range increased from 2,100 m to 3,000 m. Effectively, the APFSDS round offered a more accurate round at the price of only a small reduction in penetration which could still pose a theoretical threat to tanks like the T-55 family and the M48 Patton.

Development and Testing

Development of the APFSDS round started at an unknown date, but due to the dates available on later images and Engesa’s tendency to quickly design and develop new equipment, it is thought development started in 1984. At this point, Engesa would have had some experience in the role of APFSDS in armored vehicle design with the EE-T1 Osorio tank project which started in 1982. Additionally, the Brazilian subsidiary Engequímica, which designed the ammunition, was founded in 1984.

Engequímica designed a saddle/spool type APFSDS round in accordance with NATO style APFSDS rounds of the time period. The engineers supposedly considered both steel and tungsten for the penetrator, but went with the more capable tungsten in the end. This would be essential, considering the penetration gap to be bridged between the APFSDS and HEAT rounds for the APFSDS to be a viable option.

The tungsten penetrator had a 16:1 L/D ratio, with a diameter of 20.2 mm (0.8 inches) and a length of about 323 mm (12.7 inches). The penetrator and sabot combined weighed 2.9 kg and the sabot itself 1.8 kg. The sabot was most likely made from aluminum, like most other sabots were, making up about 38% of the projectile launch weight. The sabot weight was on the heavier side of the spectrum, as sabots tended to weigh about 30 to 39% of the total projectile launch weight at the time.

As previously mentioned, development likely started in 1984, and an image dated in October at an unknown year may suggest that live firing trials with the new round were initiated around that period. This is because later images of testing appeared in May 1985 and the testbed appeared in July 1985. Considering no APFSDS acquisition was requested after the testbed was presented, it is assumed that further development of the APFSDS round was canceled. This is further supported by an ex-Engesa employee noting that they never fixed some of the design issues, suggesting that the development was shelved as no interest was shown.

A Matter of Muzzle Brakes

The image of testing in October also excellently illustrates one of the main issues of APFSDS ammunition for light weight platforms. In the image, the standard triple baffle muzzle brake was placed on the ground and a so-called pepper pot muzzle brake was mounted on the gun instead. Complicated multi-stage muzzle brakes tend to interfere with the proper separation effect of the sabot, as the sabot would start to separate prematurely inside the muzzle brake.

Ex-Engesa employee Edson Kiyohara, assigned to the Engequímica program, noted that they tested the APFSDS rounds on both muzzle brakes to see if the triple baffle muzzle brake could be used. According to him, Engequímica first tested the standard Cascavel muzzle brake, but that the muzzle brake was damaged by the sabot separating inside.

As a result, Engequímica switched to the much simpler pepper pot muzzle brake, which is not much more than a steel tube with holes drilled into it to redirect the propellant. Since the pepperpot effectively acted as an elongation of the gun barrel, the sabot would not separate in the muzzle brake, as it would not get the required space to split. However, due to its simple nature, the effectiveness of limiting the gun recoil force was reduced compared to the standard muzzle brake. As a result, premature wear or a less comfortable vehicle for the crew to be in while firing the gun would be the compromise. Additionally, the increased trunnion pull force would also mean that the gun became less suitable for lighter vehicles, although this was less of a problem for the EE-9.

Had the APFSDS round for the EE-9 actually caught on, it would not be surprising if Engequímica would have switched to the single baffle muzzle brake, as on the French guns, of which the 90 mm F4/CN90 BR3 on the Tamoyo 1 tank was an excellent example. Supposedly, these muzzle brakes were more effective than the simple pepper pot muzzle brakes. Eventually, Engequímica could also have taken inspiration for a more advanced pepperpot design as on the B1 Centauro, as Engequímica would use the same 105 mm OTO-Melara gun on the EE-18 Sucuri tank destroyer.

Further Testing

Further testing of the APFSDS round itself seems to have been carried out in May 1985, as multiple images appear of the gun and the round at the Marambaia testing grounds. The tests included penetration tests and sabot separation tests, according to an Engesa/Engequímica employee present.

The sabot separation tests seem to have not been much more than a mesh fixed to a wooden frame at which the APFSDS round was fired. The goal of the test was to see if the sabot separated more or less equally and this could be tested to by observing if the distances between the projectile in the middle and the three sabot spreads was more or less equal. In the image available, the APFSDS round fired showed a satisfactory sabot spread.

The penetration tests were essentially firing the APFSDS round at a target consisting of a number of spaced steel plates. The gun was mounted in a static gun mount which was positioned 250 meters away from the steel plates. Each steel plate was 25 mm thick and placed vertically with a gap of 25 mm of air in between each plate. This would dampen the kinetic energy and blunt the APFSDS round as it would be subjected to various impact shocks while going through the plates. As a result, the APFSDS round managed to penetrate just 2 plates during this test.

Interestingly, this test seems to undercut Engesa’s brochure claim that the APFSDS round could penetrate a triple medium NATO target at point blank range. For a triple medium target, the round would have to penetrate a 10 mm, a 25 mm and finally a 60 mm plate. Considering the 25 mm plate penetration tests were done at 250 m on a 90 mm gun, this would have been the equivalent of a point blank test.

The claim that the APFSDS round could penetrate a NATO single Medium target was not, however, impossible. The previously mentioned similar Cockerill round was rated to be able to defeat 100 mm of steel armor at 60° at 1,000 m. Considering NATO penetration standards required 50% of the rounds to go through to rate it at a penetration, it would not be unfeasible if Engesa simply listed the higher potential estimate to make the round look more appealing on paper.

Presentation of the EE-9 APFSDS Testbed

In July 1985, an Iraqi delegation visited the Marambaia proving grounds to receive a presentation of the various projects which Engesa was carrying out for Iraq and other countries at the time. Among the vehicles presented were the prototype ET-25 armed Cascavel on the standard hull, the EE-9 with the pepper pot muzzle brake for the APFSDS test batch, and the EE-T1 P0 Osorio mock-up.

The vehicles were shown and some test firing was carried out. It does seem that Iraq had no real interest in the APFSDS round, as no further images of the EE-9 with the pepper pot muzzle brake seem to have appeared and the APFSDS round development never got further than the initial test batches. It is quite likely that the lack of interest of the Iraqi delegation in the round would have caused further development of the round to have been shelved until a customer showed serious interest in acquiring it again.

EE-9 M4 APFSDS Testbed in Detail

The EE-9 M4 APFSDS testbed weighed around 12.5 tonnes (13.8 US tons) combat-loaded. It was an estimated 6.3 m (20.7 feet) long including the gun and 5.25 m (17.2 feet) without the gun. It was 2.59 m (8.5 feet) wide, about 2.29 m (7.5 feet) tall to the top of the turret and 2.6 m (10.5 feet) tall to the top of the ET-7.62 commander’s cupola. The EE-9 M4 had a crew of three, consisting of the commander/loader (turret left), gunner (turret right), and the driver in the middle front hull.

Hull

The hull of the EE-9 M4 was manufactured from welded bimetallic steel plates. The hull also featured two covers which were mounted on the hull above the Boomerang suspension, effectively functioning as mudguards and very minor spaced armor. These mudguards could also have recesses in the middle, as on the Iraqi EE-9 M4s, to stow additional jerrycans.

The front upper hull plate presented 16 mm (0.63 inches) of bimetal armor at an angle of 60º. The sides and rear were 8.5 mm (0.33 inches) thick at varying angles, and the top and bottom hull were 6.5 mm (0.26 inches) thick. The front of the EE-9 was meant to protect from .50 caliber machine gun fire at an unknown range, while the entire vehicle was protected from 7.62 mm AP rounds at 100 m (109 yards), and standard 7.62 mm rounds at 50 m (54 yards).

The average effectiveness of the bimetallic plates was about 1.8 times the thickness of an equivalent homogeneous plate against 7.62 mm or 1.5 times the thickness against .50 caliber machine gun fire. This meant that, against .50 caliber machine gun fire, a 16 mm bimetallic plate could be used instead of a 25 mm homogenous steel plate. These protection advantages over homogenous plates effectively meant that the Cascavel saved a lot of weight without compromising protection. The outer layer would shatter and blunt the incoming projectile, while the inner layer would relatively move with the bullet, slowing it down and stopping it without shattering.

The EE-9 M4 had two headlights and black-out lights integrated in both sides of the lower front plate. A rearview mirror could be mounted on both sides of the upper front plate. Below the driver’s vision block was a foldable windshield, which the driver could use when driving with an open hatch. The driver had access to 3 periscopic sights mounted in a sort of vision block in front of him. The driver’s rotating sliding hatch was part of the top plate and was located behind the vision blocks. These periscopes and other periscopes or sights would not have been active or passive night vision equipment unless the Cascavel was ordered with these devices. The standard periscopes were manufactured by D.F. Vasconcellos.

A ventilation inlet was installed on both upper hull side plates. These ventilation inlets are recognizable by their frustum shape. A siren was installed behind the ventilation inlet on the right side of the vehicle. The fuel tank cap of the Cascavel was located on the left side, in the middle of the upper side hull plate, with the fuel tank installed on the hull floor. The EE-9 had a large ventilation grille on the rear of the vehicle, reminiscent of the M8 Greyhound, and had a rear light on both sides of the ventilation grill. The engine could be accessed through two large hatches on the hull top rear. The engine exhaust was located on the top right rear plate, as was unique to the EE-9 M4s.

The M4 used an adjustable ZF 8062 hydraulic powered steering wheel and had two pedals: the throttle on the right side of the steering wheel, and the brake to the right of the throttle. The gear selector was located to the right of the driver and the hand brake was located to the left. A control panel was located on the front left of the driver for, among other things, the headlamps, siren, windshield, the various meters, and interior lighting. To the right was the pressure selector for the central tyre inflation system.

Mobility

The EE-9 M4 used the Detroit Diesel 6V53N V6 engine, which produced 212 hp at 2,800 rpm and 598 Nm at 1,800 rpm. The engine had a total cylinder capacity of 5.212 liters, with a cylinder diameter of 98 mm and a stroke of 114 mm. The M4 Cascavel had a top speed of 95-100 km/h (59 mph) and an operational range of 750 km (466 miles).

It had a turning radius of 8.12 m (8.88 yards) and it could ford a depth of 1 m (3.3 feet) without additional preparation. The Cascavel could climb a 65º slope, could climb a vertical obstacle of 0.60 m (2 feet), cross a 1.65 m (5.4 feet) trench, and had a ground clearance of about 0.5 m (1.6 feet). The front-wheel could travel for 0.2 m (0.66 feet), while the rear wheels could travel for 0.9 m (3 feet). It used 12 x 20 run-flat tires which were 0.5 m (1.6 feet) wide. The EE-9 M2 had a distance between the front axle and rear axle of 3.05 m (10 feet), and a distance of 1.4 m (4.6 feet) between the two rear wheels.

The EE-9 M4 used an automatic Detroit Allison MT-643 transmission with four forward and one reverse gears. The transmission system could handle up to 250 hp and was the only transmission used in the EE-9s which could mount the Detroit 6V53 engine. The M7s would also use this transmission, but they were never paired with a Detroit when they were sold by Engesa.

In addition, the Cascavel used an Engesa 2 speed transfer case, which allowed the Cascavel to be used in reduced and high gear. By putting the Cascavel in reduced gear, horsepower was sacrificed for increased torque, making it more effective in climbing slopes. The vehicle was 6 x 6 driven, of which the rear 4 wheels were part of the Boomerang suspension. The Boomerang suspension, in combination with the Engesa 2 speed transfer case, enabled the Cascavel to cross challenging terrain and provide maximum traction in most situations.

The power of the engine was distributed to a differential on the front side of the vehicle, and a differential in the rear. The rear differential drove the Boomerang suspension with a single axle, which made the Boomerang suspension such an ingenious design.

In 1969, this suspension was invented by Engesa to enable trucks to transport oil to the refineries through rough terrain with bad infrastructure. With this suspension, the trucks could traverse otherwise untraversable hills for conventional suspension systems, as the wheels would always stay in contact with the ground to provide maximum traction.

The suspension system was a two wheeled-single axle driven suspension. The advantage of the Boomerang suspension was that it could be fitted on existing differentials with a single axle. Normally, this meant that the single axle, designed for the torsion forces of a single wheel, was subjected to the torsion forces of two wheels. Through excellent engineering, half of the torsion forces of the two wheels were mitigated by the suspension system built around the original axle. This design not only enabled the drive of two wheels by a single axle but, with clever usage of gears and bearings on both the axle and tube around the axle, the suspension system can rotate around its axle for 360º. This ability to rotate in extreme angles would enable the vehicles to traverse very difficult terrains and still provide maximum traction, as the suspension system curved with the terrain so that all the wheels were always in contact with the ground.

The Boomerang suspension used leaf springs for dampening. The two front wheels were used for steering. The wheels on the Boomerang suspension all rotated at the same speed. The front wheels were dampened by large coil springs. The vehicle used hydraulic disc brakes, and was steered with hydraulics as well.

A Central Tyre Inflation System (CTIS) came standard with the M4s. This system would help in obtaining the appropriate traction at various speeds by regulating the tyre pressure. This could help in crossing rough terrain but also save fuel. This was done by the driver through a switch. A Bendix Tu-flo 500 air compressor was used to provide the air flow and pressure for the CTIS.

Turret

The EE-9 APFSDS testbed used an all-welded bimetallic steel construction to protect against small arms fire. The ET-90 II turret had 16 mm of armor at the front and 8 mm of armor at the sides, rear, and top. The turret had a hatch for the commander/loader on the left and the gunner on the right. The commander’s position could also incorporate the ET-7,62 commander’s cupola. The turret had access to a pistol port on the left side to remove spent casings from the turret, and 3 smoke launchers on each side rear of the turret. Additionally, the turret was provided with 4 lifting hooks, an illumination lamp at the front and a stowage rack on the rear.

The ET-7,62 commander’s cupola was armored with 8 mm bimetal steel plates angled at 15° from vertical minimum and had a 680 mm diameter turret ring. It mounted a gun mount for a 7.62 mm machine gun, although the EE-9 APFSDS used an ET-50 gun mount for a .50 caliber machine gun instead. This seems fairly characteristic for the Iraqis at the time, who were said to have a preference for using heavy machine guns against helicopter ambushes of the Iranians during the Iraq-Iran war. The machine guns could be fired remotely from the inside and were provided with a reticule in the sight, but also a simple steel ring in front of the middle sight. The cupola had access to 5 sights, of which the middle front sight could use an SS-130 day-night sight. The SS-130 sight was an image intensifier sight with no magnification. The commander also had access to two periscopes on the front sides, and direct vision sights on the rear sides. The commander used a manual drive to rotate the cupola.

The gunner was located on the right and had access to a day/night sight for the main gun. This was an SS-122 sight on the Cascavels, an image intensifier sight which provided 10x magnification for the day sight and 9x for the passive night vision channel. The sight mirrors were coupled to the main armament to allow for automatic elevation of the sight mirrors in accordance with the gun elevation.

The commander was also the loader of the vehicle, having 12 rounds located in the turret bustle on the left side and 12 rounds in two 6-round revolver style magazines behind both the gunner and commander/loader. He had 8 boxes of machine gun ammunition in front of him and another box to his rear. The coaxial machine gun was located to the left of the gun, in front of the commander/loader and also housed a box of ammunition, for a total of 11 boxes when including the machine gun on the commander’s cupola.

The electronics, like intercoms, control boxes for the sights and switches were located to the right of the gunner, while the radios were located in the turret bustle. The SS-122 sight was in front of him, with a control box for a laser rangefinder to his front left. As the EE-9 APFSDS testbed did not mount a laser rangefinder on top of the gun, it is unclear if the control box was in the vehicle. It is likely that Engesa did not mount it, as the vehicle was only used for test firing at a range with the distances already known. The gunner had access to 3 more periscopes, of which 2 were located on the side of the turret and 1 to the rear of the gunner. The gunner used manual drives to elevate the gun and to rotate the turret. Although Engesa did market an electric drive system, it is unknown if this system was ever sold to any country.

Armament

The EE-9 APFSDS testbed used a modified EC-90 III cannon as its main armament. The EC-90 was a licensed production of the 90 mm Cockerill Mk.3 gun, obtained in 1975, and was 36 calibers long. This resulted in a barrel length of 3.24 meters (10.6 feet) excluding the muzzle brake. As the muzzle brake was replaced with a less efficient one to enable the use of APFSDS, it was quite likely that the recoil force increased as a result. It would have been possible to increase the gun recoil stroke from the standard 500 mm to 530 mm (19.7 inches to 20.9 inches) to help mitigate the inefficiency of a pepperpot muzzle brake design.

EE-9 M4 APFSDS testbed ammunition
Round	Capability	Maximum range	Velocity
APFSDS (Armored Piercing Fin Stabilized Discarding Sabot)	100 to 130 mm at 60° from vertical at 1,100 meters.	3,000 meters (3,280 yards)	1,175 m/s
HEAT – NR 478A1 (High Explosive Anti-Tank)	250 mm-300 mm (9.8-11.8 inches) flat at any range and 130 mm at 60° from vertical at any range.	2,000 meters (2,185 yards)	890 m/s
HESH – NR 503A2 (High Explosive Squash Head)	Meant for bunkers, walls and light vehicles.	2,000 meters (2,185 yards)	800 m/s
HE – NR 501A1 (High Explosive)	Lethal radius of 15 meters (16 yards)	1,600 meters (1,750 yards)	700 m/s
White Phosphorus – Smoke – NR 502A2	50 meter wide smoke screen for 20 to 30 seconds	1,600 meters (1,750 yards)	695 m/s
HEAT-TP – NR 479A2 (High Explosive Anti-Tank – Training Projectile)	Inert (no explosive filling)	2,000 meters (2,185 yards)	750 m/s

The firing table and the ‘crosshair’ of the direct-fire telescope for the EC-90 gun went up to 3,000 m for the HEAT round, 2,380 m for the HE and smoke round, and 1,020 m for the coaxial machine gun. The main armament was fired with a pedal on the turret basket floor and could be cut off through the main electrical system box. This box controlled things such as the ability to fire the main and coaxial armament, configure the ventilation system, and internal lights. In some EE-9s, the firing table was added as a plate on the electrical system box as well. The electrical system box was mounted to the right of the gunner. Additional control boxes would be added for equipment such as laser rangefinders and day/night sights if needed.

The ET-90 II turret of the APFSDS testbed used a 7.62 mm FN MAG M971 machine gun as its coaxial armament and had a .50 caliber machine gun mount on the ET-7.62 commander’s cupola. In theory, the M971 could fire up to 1,000 rounds per minute, while the practical rate of fire was about 600 rounds per minute. Its maximum practical range was 1,200 m and it weighed 2.8 kg. The coaxial machine gun was installed on the commander’s side, as the commander acted as the loader, but was fired by the gunner through a button on the main gun’s elevation handle. It could be manually fired by the commander if needed. The gun had an elevation of 15° and a depression of -8°. The EE-9 carried 2,200 rounds of 7.62 ammunition, divided between 11 cases, and a total of 44 rounds for the main gun, of which 20 were stored in the hull and 24 in the turret.

Cancellation and Unsolved Issues

When the APFSDS round development was exactly canceled is unknown. Considering the Iraqis did not seem to take interest in it in July 1985, it is quite likely the APFSDS round development was canceled soon after, as they would be Engesa’s most likely buyer for the APFSDS. It is also a possibility that the Iraqis did not have the money to acquire such a niche round as, from 1985 on, the Iraqi finances started to gradually run out due to the Iraq-Iran War. According to one of the engineers who worked on the project, a number of issues with the APFSDS round were never resolved.

The rifled gun posed a number of challenges for the APFSDS round to work properly, as the round was not supposed to spin when leaving the barrel. The rifling meant that pressure had to be limited, but it also damaged the so-called nylon obturator ring holding the sabot together and supposedly the sealing ring. Another challenge was finding out the proper depth for the so-called buttress threading on which the sabot is placed to allow it being forced through the barrel by the pressure, but also split when the projectile leaves the barrel. When machined too shallow, the sabot would not split, but when machined too deeply, the sabot would split too early in the barrel. The engineer was convinced they could have fixed these issues, had the project not been canceled. Additionally, it would be quite likely that, had the project gone through, Engesa would have offered a more efficient muzzle brake design than the pepperpot.

Why exactly the project was canceled is unknown as well, but a number of indicators point towards multiple reasons on why a customer would prefer to stick with the HEAT ammunition instead. The first is that the APFSDS round does not offer any penetration performance advantage over the HEAT round. It was more accurate and offered a better effective range, but it can be questioned how much the increased effective range would actually be utilized, as the penetration performance would drop further as well. Additionally, and perhaps the main reason, the APFSDS round would have cost about US$630 each, compared to about US$460 for the HEAT round. This meant that a customer would be paying US$170 more for a less versatile and worse performing round for a little increased accuracy and range, of which the latter may or may not be used too much.

While Engesa never seems to have considered this, it would have perhaps been a better idea if it had started offering a more anti-tank focused gun instead for the EE-9. These could have been the 60 mm HVMS, although this gun lacked the ammunition versatility of the EC-90, or, perhaps more competitively, the 90 mm F4. The 90 mm F4 was a high pressure and high velocity gun which was already in Brazil in 1984, as it was mounted on the Tamoyo 1 in 1984. The 90 mm F4 was also mounted on the French ERC-90 Sagaie 6×6 wheeled vehicle, which meant that the EE-9 could have directly competed with it. In essence, the 90 mm F4 used the same ammo as on the French 90 mm D921, but also introduced an APFSDS round. As such, Engesa could have simply refitted their existing projectiles for his gun as well, but with modified casings.

However, from a different point of view, most of the larger Sagaie sales already happened at the turn from the 70s to the 80s and only about 20 were sold after 1984. Additionally, the Sagaies could be sold with much more advanced systems, like stabilization, a linked fire control system, a semi-autoloader, and electro-hydraulic turret drives. The EE-9 would either have to be sold with a similar fire control system or be sold as a cheap and simple upgunned competitor instead.

The fate of the EE-9 M4 APFSDS testbed is unknown. It is likely that it remained as a test vehicle for Engesa with the pepperpot muzzle brake removed, but its fate after Engesa’s bankruptcy is unknown. It was likely either sold to one of the legacy companies, like Universal or Columbus, scrapped, or potentially sold to Iraq in the last batch of EE-9s sold in 1985. A number of Engesa vehicles, like both Osorio tanks and the EE-3 Jararacas, would initially end up with the 13th RCMec in Pirassununga, but this does not seem to have happened with the testbed.

Conclusion

In the end, the costs of the APFSDS round for the EE-9 simply outweighed the minor benefits it brought to the table. The performance was lacking and the price tag did not justify the increased accuracy and extended range compared to the HEAT ammunition. It would have perhaps been more effective if Engesa had decided to offer a more dedicated anti-tank version, although this would have been a much more expensive vehicle with perhaps a very limited market. An APFSDS shooting EE-9 ended up as a dead end.

Specifications (EE-9 M4 ET-25)
Dimensions (L-W-H)	6.3 x 2.59 x 2.29 m (20.7 x 8.5 x 7.5 feet)
Total weight	12.5 tonnes (13.8 US tons)
Crew	3 (driver, commander, gunner)
Propulsion	Detroit Diesel 6V53 212 hp engine (or OM352A 172 hp engine)
Speed (road)	95-100 km/h (59 mph)
Operational range	750 km (466 miles)
Armament	90 mm KBA cannon 7.62 mm FN MAG (coaxial) Optional .50 machine gun (turret top)
Armor	Hull Bimetal Front 16 mm (0.63 inches) Side 8 mm (0.32 inches) Rear 8 mm (0.32 inches) Top 6.5 mm (0.26 inches) Floor 6.5 mm (0.26 inches) ET-25 turret (Estimated) Front 16 mm (0.63 inches) Side 8 mm (0.32 inches) Rear 8 mm (0.32 inches) Top 8 mm (0.32 inches)
Produced	1

Special thanks to Expedito Carlos Stephani Bastos, the leading expert of Brazilian armored 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.

Sources

Engesa EE-9 Cascavel 40 anos de combates 1977-2017 – Expedito Carlos Stephani Bastos
Brazilian Engesa EE-9 Cascavel 6×6 at war 1977-2020 – Expedito Carlos Stephani Bastos
Blindados no Brasil – Expedito Carlos Stephani Bastos
Engesa manuals
Engesa brochures
Dual Harness skin stops armor-piercing projectiles Article of Richard M. Ogórkiewicz
Technology of Tanks – Richard M. Ogórkiewicz
Personal correspondence with Ex-Engesa Employees
Personal correspondence with Expedito Carlos Stephani Bastos
Personal correspondence with Paulo Roberto Bastos Jr.