The Chieftain design included a heavily sloped hull and turret which greatly increased the effective thickness of the frontal armour - 388 mm (15.3 in) on the glacis (from an actual thickness of 120 mm (4.7 in)), and 390 mm (15.4 in) on the turret (from 195 mm (7.7 in)). It had a mantleless turret, in order to take full advantage of reclining the vehicle up to ten degrees in a hull-down position. The driver lay semi-recumbent in the hull when his hatch was closed down which helped to reduce overall height. The commander, gunner and loader were situated in the turret. To the left side of the turret was a large infra-red searchlight in an armoured housing. The suspension was of the Horstmann bogie type, with large side plates to protect the tracks and provide stand-off protection from hollow charge attack.
| FV 4201 Chieftain MBT | |
|---|---|
| Type | Main battle tank |
| Place of origin |  United Kingdom |
| Service history | |
| In service | 1966–1995 |
| Used by | UK, Iran, Iraq, Jordan, Kuwait, Oman |
| Wars | Iran–Iraq War, Iraq-Kuwait War |
| Production history | |
| Manufacturer | Leyland Motors |
| Specifications | |
| Weight | 55 long tons (62 ST; 56 t) |
| Length | 7.5 m (24 ft 7 in) - hull |
| Width | 3.5 m (11 ft 6 in) |
| Height | 2.9 m (9 ft 6 in) |
| Crew | 4 |
| | |
| Armour | Glacis: 120 mm (72º) Hull sides: 38 mm (10º) Turret: 195 mm (60º) |
| Main armament | L11A5 120 mm rifled gun |
| Secondary armament | 2 x L7 MG |
| Engine | Leyland L60 (multifuel compression-ignition) 750 hp (560 kW) |
| Suspension | Horstmann |
| Operational range | 500 km (310 miles) on roads |
| Speed | Road: 48 km/h (30 mph) Off road: 30 km/h (19 mph) |
The Leyland L60 engine is a two-stroke opposed piston design intended for multi-fuel use so that it could run on petrol or diesel or anything in between. In practice the engine did not deliver the expected power, and was unreliable, estimated to have a 90% breakdown rate, but improvements were introduced to address this. Primary problems included, cylinder liner failure, fan drive problems and perpetual leaks due to vibration and badly routed pipework. However, as the engine power improved the tank itself became heavier. The tank was steered by conventional tillers hydraulically actuating onto external brake discs. The discs worked via the epicyclic gearbox providing "regenerative" steering. In reality the discs and pads became soaked in oil and diesel and the steering became difficult. The gearbox was operated motorcycle-style with a kick up/kick down "peg" on the left which actuated electro-hydraulic units in the gearbox; the accelerator was cable operated by the right foot. In the turret the loader was on the left and the gunner on the right of the gun with the commander behind the gunner.
The main armament was the 120 mm L11A5 rifled gun. This differed from most contemporary main tank armament as it used projectiles and charges which were loaded separately, as opposed to a single fixed round. The charges were encased in combustible bags. (Other tank guns, such as the Conqueror, had to store the spent shell cartridges or eject them outside.) The combustible charges were stored in 36 recesses surrounded by a water/glycerine mixture - so-called "wet-stowage". In the event of a hit which penetrated the fighting compartment, the jacket would rupture, soaking the charges and preventing a catastrophic propellant charge explosion. The gun itself could fire a wide range of ammunition, but the most commonly loaded types were high explosive squash head (HESH) or armour-piercing discarding sabot (APDS), or practice round equivalents for both types. When the Chieftain was first introduced, a 12.7 mm ranging gun was mounted above the main gun. This fired ranging shots out to a maximum of 2,600 yards (2,400 m), at which point the tracer in the ranging rounds burned out. Later, in the late 1970s and early 1980s, a Barr and Stroud laser rangefinder replaced the ranging machine gun. This allowed engagements at much longer ranges, and also could be linked to the fire control system, allowing more rapid engagements and changes of target. The gun was fully stabilised with a fully computerized integrated control system. The secondary armament consisted of a coaxial L8A1 7.62 mm machine gun, and another 7.62 mm machine gun mounted on the commander's cupola.
