Chieftain (tank)
The FV4201 Chieftain was the main battle tank of the United Kingdom during the 1960s-1990s. A development of the Centurion, the Chieftain introduced the supine (reclining) driver position to British design allowing a heavily sloped hull with reduced height. A new powerpack and improved transmission gave it higher speed than the Centurion despite being heavier due to major upgrades to armour protection and the armament: this allowed it to replace both the Conqueror and Centurion while performing their roles effectively. It remained in service until replaced by the Challenger 1 which shared many of the Chieftain's features . Development. The Chieftain was an evolutionary development of the successful cruiser line of tanks that had emerged at the end of the Second World War. Its predecessor, the Centurion main battle tank (MBT), is widely considered to be one of the most successful of post-war MBT designs. However, the introduction of the Soviet IS-3 /IS-4 heavy tank along with Soviet T-54/T-55 forced the introduction of the Conqueror heavy tank armed with a gun. A single design combining the firepower of the Conqueror's 120 mm gun with the mobility and general usefulness of the Centurion was seen as  the ideal combination. Leyland, who had been involved in the Centurion tank, had built their own prototypes of a new tank design in 1956. Several aspects of the design were trialled by the production of the FV4202 "40-ton Centurion" with a reclined driver position and mantletless gun mounting. In effect, the FV4202 was a shorter Centurion chassis with a prototype of what would become the Chieftain turret, but armed with the 20pdr gun. This work led to a War Office specification for a new tank. The General Staff specification drew on the experience of Centurion tanks in the Korean  War as well as that of the Conqueror tank. The tank was expected to be able to engage the enemy at long range, from defensive positions, and be proof against medium artillery. To this end, the gun was to have a greater angle of depression than the 8 degrees of Conqueror and would be equipped with better frontal armour. The tank was expected to achieve a firing rate of 10 rounds per minute in the first minute and six per minute for the following four. The first few prototypes were provided for troop trials from 1959 which identified a number  of changes. Improvements to address engine vibration and cooling resulted in a redesign of the rear hull. This increased the design weight to nearly 50 tons and accordingly the suspension (which had been designed for 45 tons) was strengthened. Trackpads had to be fitted to protect roads from damage and the ground clearance increased. The design was accepted in the early 1960s. Britain and Israel had collaborated on the development in its latter stages with a view to Israel purchasing and domestically producing the vehicle. Two prototypes were delivered as part of a four-year trial. However, it was eventually  decided not to sell the marque to the Israelis (since, at that period of time in the late 1960s, the UK was more friendly towards the Arab states and Jordan than to Israel), which prompted them to follow their own development programme. In 1957, NATO had specified that its forces should use multi-fuel engines. The early Leyland engine delivered around to the sprocket, which meant a top road speed of around and cross-country performance was limited. This was further hampered by the Horstmann coil spring suspension, which made it a challenge to drive cross country and provide the  crew with a comfortable ride. Due to the cylinder linings being pressure fitted, coolant leaks within the cylinder block were common, resulting in white smoke billowing from the exhaust. In the late 1970s, engine design changed with the introduction of Belzona which was used to improve the lining seals. Engine output also increased, with later engines delivering some to the sprocket. This meant better performance and an increased speed. However, cross-country performance remained limited. Design. The design of the Chieftain included a heavily sloped hull and turret which greatly increased the effective thickness of the frontal armour – on the  glacis (from an actual thickness of ) and on the turret (from ). It had a mantletless turret in order to take full advantage of reclining the vehicle up to ten degrees in a hull-down position. For security reasons early prototypes had a canvas screen covering the mantlet and a sheet metal box mounted over the sloping glacis plate to disguise the configuration of the vehicle. The driver lay semi-recumbent in the hull when his hatch was closed down which helped to reduce the profile of the forward glacis plate. The commander, gunner and loader were situated in the turret . To the left side of the turret was a large searchlight with infrared capability in an armoured housing. The Leyland L60 engine is a two-stroke opposed piston design intended for multi-fuel use so that it could run on whatever fuel was available. 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. The Merritt-Brown TN12 triple-differential 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 cable was 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 situated behind the gunner. The suspension was of the Horstmann bogie type with large side steel plates  to protect the tracks and provide stand-off protection from hollow charge attack. The main armament was the 120 mm L11A5 rifled gun. This differed from most contemporary main tank armament as it used projectiles and charges that were loaded separately, as opposed to a single fixed round. The charges were encased in combustible bags. Other tank guns such as the 120mm L1 gun on the Conqueror, needed to store the spent shell cartridges or eject them outside. The combustible charges were stored in 36 recesses surrounded by a pressurised water/glycol mixture – so-called "wet-stowage". In the  event of a hit penetrating the fighting compartment, the jacket would rupture soaking the charges and preventing a catastrophic propellant explosion. As there was no shell case, the firing of the charge was by vent tubes automatically loaded from a ten-round magazine on the breech. Due to the length of the gun, which required balancing, and the need for storage space, the turret has a large overhang to the rear. This contains radios, ammunition and fire control equipment and has further stowage externally. The gun could fire a wide range of ammunition but the most commonly loaded types were  high explosive squash head (HESH), armour-piercing discarding sabot (APDS), or practice round equivalents for both types. The Chieftain could store up to 64 projectiles (though a maximum of 36 APDS, limited by the propellant stowage). 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. An advantage of using two-part ammunition was that in the case of inert rounds like APDS the loader could reach for the next round and hold it  in his lap, ready to load while the gunner was acquiring the target and firing. This practice increases the rate of fire but would be hazardous with one-piece ammunition. Chieftain had an NBC protection system which Centurion lacked. An infantry telephone was fitted to the rear of the tank to facilitate communication with infantry. The initial Fire-control system (FCS) was the Marconi FV/GCE Mk 4. A .50-inch (12.7 mm) ranging gun was mounted above the main gun (with 300 rounds available). This fired ranging shots out to a maximum of , at which point the tracer in  the ranging rounds burned out although the high explosive tip still created a visible "splash" on impact. The tank commander had a rotating cupola with nine vision blocks -giving all round view, plus the 7.62 mm machine-gun and an infrared (IR) capable projector coaxial with the weapon. The aiming systems were provided for both the gunner and the tank commander; they had 1x or 10x selectable magnification power, increasing to x15 in the Mk5 and beyond, and they were replaceable with IR vision systems for night operations (3x magnification power). The commander could rotate his cupola to bring his  sight onto a target and then engage the mechanism that brought the turret round on to the correct bearing so that the gunner could complete the aiming. The commander's controls had over-ride capability on those of the gunner. The left side of the turret had a large searchlight with an electrically controlled infrared filter inside an armoured box, with a relatively long range – up to . From the beginning of the 1970s, the Mk 3/3 version replaced the ranging gun with a Barr and Stroud LF-2 laser rangefinder with a range. 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. On later models, fire control was provided by the Marconi IFCS (Improved Fire Control System), using a digital ballistic computer. The upgrade was not finished until the end of 1980, when some examples (but not the majority) had the IR searchlight replaced with TOGS. Many later examples had Stillbrew armour, intended to defeat Soviet 125 mm tank guns and heavy anti-tank missiles. These became the Mark 11 version. Service. Chieftain equipped British units of the British Army of the Rhine (BAOR) during  the Cold War, defending West Germany against possible Warsaw Pact attack. Like its European competitors, Chieftain found a large export market in the Middle East, but unlike Centurion, it was not adopted by any other NATO or Commonwealth country. Chieftain proved itself capable in combat and able to be upgraded, both for overall improvement and to meet local requirements. It was continuously upgraded until the early 1990s, when it was replaced by Challenger 1. The final Chieftain version, which was used by the British Army until 1995, incorporated "Stillbrew" armour named after Colonel Still and John Brewer from the Military  Vehicles and Engineering Establishment (MVEE), the Improved Fire Control System (IFCS) and the Thermal Observation Gunnery Sight (TOGS). The last British Regiment equipped with Chieftain was the 1st Royal Tank Regiment, which was based at Aliwal Barracks, Tidworth. The first model was introduced in 1967. Chieftain was supplied to at least six countries, including Iran, Kuwait, Oman and Jordan. An agreement for sales to Israel and local production was cancelled by the British Government in 1969, despite considerable Israeli technical and tactical input into the development of the tank, especially the capacity to operate successfully in desert environments, and the  provision for the tank to make good use of hull-down positioning. Two examples were delivered to and extensively trialled by the Israeli Armoured Corps. This experience spurred the creation of the indigenous Israeli Merkava, the development programme of which was led by General Israel Tal, who had worked closely with the British in the Anglo-Israeli Chieftain project. The largest foreign sale was to Iran, which, at the recommendation of General Tal, took delivery of 707 Mk-3P and Mk-5P (the letter P standing for Persia), as well as 187 FV4030-1, 41 ARV and 14 AVLB before the 1979  revolution. Further planned deliveries of the more capable FV4030-2 (Shir 1) and FV4030-3 (Shir 2) series were cancelled at that point. It was in the Middle East that the Chieftain was to see all of its operational experience. First, it was used extensively by Iran during the Iran–Iraq War of 1980–88, including the largest tank battle of the war, with mixed results as the Chieftain Mk 3/5 suffered from chronic engine problems and low power-to-weight ratio, making it unreliable and slow when manoeuvering over harsh terrain, which in turn made it prone to breakdowns in  the midst of battle or a sluggish target and thus vulnerable to enemy tank fire. After the tank battle at Susangerd, captured Chieftains of the Iranian 92nd Armoured Division were taken back to Baghdad for trials. According to Aladdin Makki, the Iraqi Army Corps chief of staff in a post-war interview, Iraqi sabot rounds "Went through the front Armour of the Chieftain and came out the backside". This as well as the Chieftain's poor off-road capability influenced the Iraqis to reject British arms sale propositions, who were at the time courting Iraq for arms sales that included  Chieftain MBT's. According to Makki, when the British telephoned the Iraqi director of Armor, Salah Askar, he responded with "We don't want your stupid tanks!". Ra'ad Al-Hamdani, an Iraqi general in the Iraqi Republican Guard, also expressed negative opinion on the Chieftain's performance in combat, stating "The 16th Iranian Armored Division, which was equipped with Chieftain tanks, lost a battle against the 10th Iraqi Armored Brigade with T-72 tanks. It is hard for an armored brigade to destroy a division in 12 hours but it happened; it was a disaster for the Iranians". Out of the  894 Chieftain tanks that had started the war only 200 were left by the war's end. The Chieftain remains in service in Iran, the Mobarez tank being a locally upgraded version. Kuwait and the Battle of the Bridges. Kuwait had 143 Chieftains on the eve of the 1990 Iraqi Invasion of Kuwait. Thirty-seven Chieftains of the Kuwaiti 35th Armored Brigade fought at the Battle of the Bridges against elements of the Iraqi Hammurabi and Medina divisions before withdrawing over the Saudi border. None of the brigade's tanks was lost in the battle, and the 35th Armored Brigade  (known as Al-Fatah) became part of "Joint Command Forces East" during the 1991 Gulf War and was able to return into Kuwait undefeated. Besides those of the 35th Armored Brigade, the rest of the Kuwaiti Armed Forces' Chieftains (136) were either destroyed or captured by the invading forces after they had been abandoned by their Kuwaiti crews when their ammunition ran out. After the liberation of Kuwait, the ageing Chieftains were replaced by the Yugoslav M-84. Mark 1 and Mark 2 models had a coaxial Browning .50-inch (12.7 mm) ranging machine guns prior to the introduction of the  laser rangefinder. Variants. In 1975 all British Army earlier Marks of tanks except Mark 1's were upgraded to Chieftain Mk.5 standard as part of the 1975 "Totem Pole" programme. "Exercise Totem Pole" was carried out in six-to-nine phases depending on the Mark of vehicle being modified (Chieftain Mk.5's already had some of the required changes incorporated at the factory) between 1975 and 1979 and included fitment of the Marconi Improved Fire Control System (IFCS), replacement of the searchlight with the Barr & Stroud Thermal Observation Gunnery System (TOGS), along with modifications for using FSAPDS ammunition. Upon completion  of each phase the vehicle received an additional suffix to the designation, e.g., "Chieftain Mk.3/S(Y)2" denoting a Mark 3/S having completed the first three phases of "Totem Pole". including addition of Clansman radios, fitting of TLS, fitment of Muzzle Reference System (MRS) upon replacement of L11A3 barrel with L11A5 barrel, and fitment of 750 hp L60 Mark 8A. These vehicles were re-designated Chieftain Mk's.6 to Mk.8. In 1977 the engines of all British Army vehicles were upgraded to the 750 hp L60 Mark 9A, followed by further upgrading with the L60 Mark 11A or L60 Mark 12A  in 1978 as part of the 1977 "Dark Morn" and the 1978 "Sundance" programmes. "Exercise Sundance" concerned improvements in engine power, reliability, and other power train improvements, and was carried out in five main phases between 1976 and 1979. These, in themselves, had been preceded by "Dark Morn", "High Noon", and the initial "Fleetfoot" engine development programme which had completed in October 1971. Vehicles on which "Sundance" modifications had been carried out received an additional 'Z' suffix appended to their designations, the "Sundance" engines themselves were signified with a distinctive orange/yellow-coloured upper crankcase.