From machine-guns to armored cars
FN Herstal is a worldwide famous weapons maker, building, among others, the FN MAG machine-gun, also found in many tanks and armored vehicles. In 1960, the Belgian Gendarmerie made requirements for an armored car. The acquisition program was not closed to foreign bidders. However, FN Herstal, which had no previous experience with armored vehicles, designed one regardless, based on the FN 4RM/62 Ardennes (4 × 4) 1500 kg truck and taking inspiration from other designs, like the French Panhard AML.
The first prototype was ready in 1962, the second after modifications in 1965 and the final vehicle approved for production, which took place in 1971-72. In the meantime, the vehicle has been retired from service and FN Herstal is no longer involved in armored vehicle design.
The hull of the FN 4RM, also called the 62F AB, was made of all-welded steel. The driver sat in the center-front of the vehicle, having a single piece hatch (opening upwards) and three periscopes. He could also see through a bullet-proof window at the very front of the hatch, which had an armored cover for when the vehicle would be under fire.
A single door on either side of the hull allowed access to the vehicle, the right one being fitted with an observation port. The rest of the crew, the commander (right) and the gunner (left) were seated in the all-welded turret placed in the middle of the vehicle. Each of them had his own one-piece hatch and searchlight. The commander’s cupola had 8 vision blocks, while the gunner had three and the main gun optical sight. The turret had electric powered traverse, with two-speeds and manual backup. The crew was also protected by an NBC system.
The rear compartment housed the 130 hp gasoline engine, giving a power-to-weight ratio of 14.77 hp/ton. It was connected to a 4/1 manual gearbox and fed by petrol tanks with a total fuel capacity of 180 liters, giving a total range of 600 km. The FN 4RM could reach a top speed of 110 km/h (70 mph) on flat ground. The ground clearance was about 324 mm and the wheelbase 2.45 m. The turning radius was 6 m, and the vehicle was capable of fording 1.1 m deep water, climb a 60% gradient. The rear compartment was protected by an automatic fire-extinguishing system.
There were, in fact, two kinds of turrets. The first one was heavily armed with a 90 mm (3.54 in) CATI gun firing HEAT and shrapnel rounds. The HEAT shells had a muzzle velocity of 640 m/s and an effective range of 1000 m, able to destroy most comparable vehicles, APCs and light tanks. A 7.62 mm (0.3 in) FN MAG machine gun was placed coaxially, while another was pintle-mounted in front of the commander’s cupola. For concealment, six electrically-fired smoke dischargers were installed on either side of the turret.
The second turret model was lighter, equipped with a 60 mm (2.36 in) breech-loaded mortar and the same coaxial machine gun with independent elevation. The banks of smoke dischargers was placed more to the front.
62 FN 4RMs were manufactured in 1971-72. They served with the Gendarmerie until the 1990s. They are now retired but apparently several are in storage and running order.
FN 4RM specifications
|Dimensions||4.5 x2.26 x2.37 m
|Total weight, battle ready||8.8 tons|
|Crew||3 (driver, gunner, commander)|
|Propulsion||FN 4RM 6-cyl petrol, 130 h, 14.7 hp/ton|
|Suspension||4×4 independent coil springs|
|Speed (road)||110 km/h (70 mph)|
|Range||600 km (370 mi)|
|Armament||90 mm (3.54 in) CATI gun or 60 mm (2.36 in) breech-loaded mortar
2xFN MAG machine-guns
|Total production||62 in 1971-1972|
Mortar version of the FN 4RM in use with the Belgian Gendarmerie.
FN 4RM with the 90 mm (3.54 in) gun, Belgian Gendarmerie, 1970s