SO-76 M18 (FF)

_YugoSlav · June 16, 2025, 5:10am

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SO-76 M18 (FF)

History and Description

After World War II, numerous American M18 Hellcat tank destroyers were supplied to Yugoslavia under military aid programs. There they received the designation SO-76 M18. They remained in service with the Yugoslav People’s Army for decades, even after more modern equipment became available. By the 1990s, during the Yugoslav Wars, the original radial engines had become increasingly difficult to maintain due to extreme parts scarcity. To keep these aging platforms operational, local military units and workshops undertook several improvised field modifications. One such modification carried out by the Army of Republika Srpska involved replacing the original 460 hp radial engine with a FAMOS FF 6-cylinder diesel engine, most likely sourced from a FAP 1314 SK/A military dump truck.

This swap included not just the engine, but also the truck’s radiator, starter, engine hood and grille — all integrated into the M18’s cut hull. The original 3-speed transmission and drivetrain were most likely retained, and the vehicle’s weight remained roughly the same. The FAMOS FF truck engine produced 145 horsepower at 2200 rpm, significantly less than the original powerplant. It is unknown how efficient this setup was or if it even worked at all. But if it did, the much lower horsepower and torque output would drastically reduce the Hellcat’s acceleration and off-road mobility. Theoretically, the top speed could still approach 73 km/h based on gearing, but in practice, the converted M18 probably rarely exceeded 30–40 km/h, especially on uneven terrain. Although the elevated hood of the truck engine limited the gun’s vertical traverse angles, it didn’t prevent the turret from rotating 360 degrees (as shown in the first picture).

I’m not entirely sure which specific truck engine was used—either the FAMOS F (130 hp) or the FAMOS FF (145 hp). Civilian FAP 13 trucks with the 130 hp engine typically had the FAP 13 badge mounted on the grille, just like the one seen on the modified Hellcat. In contrast, civilian models with the 145 hp engine usually had the badge placed on the cab door under the window. However, this badge placement distinction did not apply to military trucks. Up until 1991, all military FAP 13 vehicles—regardless of engine type—had the badge on the front grille. This makes it difficult, if not impossible, to determine which engine was actually installed in the modified M18, as the Yugoslav People’s Army operated both types. That said, by the early 1970s, only the more powerful FAMOS FF engine was being installed in new military FAP 13 trucks. This suggests that, by the onset of the Yugoslav Wars, vehicles equipped with the 145 hp engine were likely more common in army service, making the FF variant a more probable candidate for the Hellcat retrofit.

According to one source a similar conversion was carried out on the Bosniak side. There, a Hellcat was successfully re-engined with a commercial Deutz diesel engine imported from Germany. These uniquely adapted vehicles are a fascinating example of field engineering under wartime constraints. They served not only as combat vehicles during the Yugoslav conflicts but also as symbols of adaptability, making do with available resources long after their original design life had passed.

Specifications

Essentials
- Length of the hull; 5.28 m
- Width; 2.87 m
- Height; less thann 2.57 m
- Mass; ca. 17.7 t
- Crew; 5
Protection
- Armor;
  - hull: 12 mm front, 12 mm side, 12 mm rear
  - turret: 25-44 mm front, 12.7 mm sides, 12.7 mm rear
- APS; N/A
- ERA; N/A
- Smoke; N/A
Mobility
- Engine; FAMOS FF, 145 hp at 2200 rpm
- Power/weight; 8.2 hp/t
- Transmission; 1 reverse gear, 3 forward gears
- Top speed;
  - theoretical: 73 km/h
  - practical: 30-40 km/h
- Amphibious; No
Firepower
- Main; 76 mm M1 cannon
  - Penetration at 10 m; 149 mm (APCBC)
  - Ammunition; 45 rounds
  - Stabilizer; No
  - Vertical guidance; -10 ° / +20 °
  - Turret rotation speed; 24 °/s