The first running prototype, without a turret, was ready in late 1959, and six prototypes with turrets were delivered for army trials in 1961-62. Various changes were introduced early on. The design originally had smaller road wheels than the Centurion, but this gave a ground clearance of only 17 inches, which proved too low. The problem was overcome by reverting to the same road wheels as the Centurion, and increasing ground clearance to 22 inches in the procerss. Rubber pads were added to the tracks to prevent damage to public roads, and the exhaust system was much modified following some technical changes to prevent the gearbox from overheating.
The characteristics of the FV4201, subsequently known as the Chieftain Main Battle Tank, have not changed greatly since its first appearance, though there have been several detail changes. The outstanding feature of the vehicle is, of course, its L11 120 mm gun. This can fire APDS (armour piercing discarding sabot), and HESH/HE (high explosive squash head/high explosive) ounds with all charges inbagged form. Fire-resistant stowage is provided for the bagged charges. A ranging machine gun is fitted integral with the main armament, and is linked to the sight with graticule marks scaled for the appropriate types of ammunition. Rapid sight correction is possible by direct observation of the rangin machine gun strikes on the target. This basically simple optical ranging technique was first developed for later marks of Centurion, and its reputation as a foolproof and accurate system has been further enhanced in the Chieftain, and has given British tank gunners a second to none record, with a good chance of a direct hit with the first round away - important considerations when ammunition capacity in the tank is limited, and when the potential enemy may have superior numbers of tanks. For indirect fire the conventional type of ranging drum and elinometer are used. A contra rotating cupola with hand traverse enables the commander to select and indicate the targets rapidly, and a sight linked to the gunner's sight enables the commander to aim the gun from the cupola position. A GP machine gun is fitted to the cupola and can be aimed and fired remotely with the cupola closed down. The commander's main binocular sight is fitted in the rotating part of the cupola with the fixed part of the cupola containing nine periscopes to give an all-round view. The gun is stabilised in elevation and the turret is stabilised in azimuth, so that the gun can be fired with a high degree of accuracy even while the vehicle is moving. There is a light projector in a box on the left side of the turret, offering either white light or intra-red light for night fighting, the system being linked for elevation with the gunner's sight enables the commander to aim the gun from the cupola position. A GP machine gune is fitted to the cupola and can be aimed and fired remotely with the cupola closed down. The commander's main binocular sight is fitted in the rotating part of the cupola with the fixed part of the cupola containing nine periscopes to give an all-round view. The gun is stabilised in elevation and the turret is stabilised in azimuth, so that the gun can be fired with a high degree of accuracy even while the vehicle is moving. There is a light projector in a box on the left side of the turret, offering either white light or infra-red light for night fighting, the system being linked for elevation with the gunner's sight. The gunner and the commander have optical infra-red converters for their sights, and the commander's spotlight can be fitted with an infra-red filter. The driver's reclining position is flanked by battery and ammunition stowage, and he has a periscope behind his hatch. There are conventional steering levers with epicyclic gearbox and Merritt differential transmission. Transmission is automatic with foot pedal gearchange selector. The superstructure overhangs the tracks to give the necessary turret ring radius. Both the hull and turret fronts are complex castings, and the hull front is said to have given some problems in the casting when production first started.
Development of the Chieftain since it entered production is best seen by summarising the various models:
Chiftain Mk. I: About 40 of these vehicles were built, largely for extended troop trials and training. After test service with 1st and 5th RTR, the type was cleared for service in 1963. A distinguishing feature was the split hatches to the cupola similar to those on later types of Centurion.
Chieftain MK. 2: This was the definitive production version which first went into service (with the 11th Hussars) in 1967. It had a one piece cupola hatch and special ventilation equipment on the turret rear to enable the vehicle to operate closed down in nuclear and biologival warfare conditions. The armour plating on the light projector was reduced, round stowage reduced, and snorkel wading equipment was supplied in place of a floatation kit originally envisaged. This type saw extensive service in the late 1960's and early 1970's, and indeed, the Chieftain rapidly replaced the Centurion as the British Army's main battle tank once production was under way. Special purpose models- a recovery vehicle, AURE, and bridgelayer have appeared.
Chieftain Mk 3: This version appeared in 1969 and had a better auxiliary generator and detail improvements to the engine. The L60 engine proved complex, and successive marks of the Chieftain have had the engine gradually uprated to give the full designed power output. An improved cupola, and modified internal stowage were other changes.
Chieftain Mk 3/3: This saw a big step forward, in that the fire control arrangements were modified so that an advanced laser sight for the gunner can be fitted.
Chieftain Mk 5: First announced in 1970, this was the main type in service in the mid 1970's. Further engine modifications bring the power output up to 750bph, with consequent improvement in overall performance, and revision of the ammunition stowage arrangements enabled 64 rounds to be stowed. Splash plates have been added on the glacis.
The Chieftain has been compared, inevitably, with the French AMX-30, the West German Leopard, and the US M60A1. All these tanks have speed and mobility superior to the Chieftain and are lighter in weight. They also have the 105 mm gun and are inferior to the Chieftain in firepower and armour. Whether mobility or firepower will be the most crucial to top quality in any European major war has yet to be put to the test, but the pace of the technology in armoured warfare is relentless. The Soviets have made big progress with fin-established ammunition (in their T-62 and new T-72 battle tanks) and the Israeli-Arab Yom Kippur war of October, 1973 showed for the first time that the main battle tank was very vulnerable to tactical anti-tank missiles skillfully employed. It may be, therefore, that the Chieftain could be the last of the traditional type of tank in the form in which it has been accepted for many years past. Whatever the future, however, Chieftain remains an exciting and powerful fighting vehicle. It has been ordered by the Iranian Army and has interested many others, though the great expense of one of these vehicles limits their availability.