Chieftain Tank Mk 11

Chieftain Tank Mk 11 at Bovington Tank Museum

The British Chieftain Tank FV4201 was the first and most powerful Main Battle Tank in NATO during the former Cold War. First deliveries to the British Army were completed in 1966 and was finally withdrawn from service in 1995 as its replacement the Challenger 2 entered service. A number of Combat Engineer Vehicles were built on the hull.

The Chieftain was modified and exported to several Middle-East countries were it remains in service and has seen active combat.

The Chieftain Tank continued to be upgraded in protection and mobility throughout the 1980’s and 90’s but these later models failed to attract any orders as newer Main Battle Tanks entered the export market.

Chieftain Tank Development

Whilst the British Centurion Medium Tank had been a great success, the development of its replacement started in 1951. Known as the “Medium Gun Tank No 2” emphasis was put on its firepower, then protection and finally mobility to insure its survivability whilst not exceeding a weight of 45 tonnes.

By 1956 concept studies by the Fighting Vehicles Research and Development Establishment (FVRDE) had looked at various gun types, propellants and calibre. These resulted in the recommendations that a 120mm bore calibre main gun would be needed to defeat current and future Soviet Heavy Tanks at the ranges initially required. These studies had also concluded that a 2 part ammunition should be used, rather than 1 part, which at 120mm would be a lot larger and heavier.

FV4202

FV4202 The 40 tonne Centurion at Bovington

Leyland (who were manufacturing the Centurion) were the prime-design contractor of the new vehicle, which was now officially designated the FV4201. The company produced 3 vehicles to test the vehicles proposed suspension (using Centurion parts), the new turret and most importantly the new drivers reclining chair in 1956. These 3 vehicles were designated FV4202 and unofficially the 40-tonne Centurion.

Traditionally a tank driver would sit up right in his station, which would require a higher steel constructed hull and thus increase the tanks weight. The new drivers reclining chair meant that he was almost lying backwards, the hull height could be reduced resulting in a lighter tank that did not exceed 45 tonne.

The FV4202 vehicles were not fitted with a gun mantle as they were not used for firing trials in the Chieftains developement. 1 still remains in storage (pictured above) at Bovington Tank Museum.

During 1957 the Chieftains development took 3 design blows. Firstly the steel armor needed to be made thicker and secondly the gun elevation on both the – and + axes had to be increased resulting in an enlarged heavier turret.

The third blow would haunt the FV4201 for some decades to come. As a member of NATO, the UK had to comply with Standardization Agreements (STANAG) and in that year a new STANAG was passed that all Fighting Vehicles engines had to be multi-fueled, that is they could run on anything from heating oil to jet-fighter fuel. Not only did this mean the original Rolls Royce engine was replaced with a modified German designed aircraft engine (later manufactured as the Leyland L60) but the hull design had to be reconfigured to fit the larger engine and pushed the vehicles overall weight pass 45 tonne.

Chieftain Tank Prototype

Chieftain Tank Prototype

In 1959 the final design wooden mock-up of the FV4201 was completed by FVRDE. Leyland had been responsable for the hull and automotive components (Self-Changing Gears ltd designed the TN12 transmission) and Vickers-Armstrong developed the turret.

In the same year six prototypes were ordered (P1 to P6) and a follow on order for an additional six (bringing the total to 12) was placed with production shared between the Royal Ordnance Factory Leeds and Vickers-Armstrong.

 Testing and trials of the prototypes started in 1960, which included firing trials of the main gun, its sub-systems and endurance trials testing the automotive components resulting in changes to the design as each prototype was built.

The initial mechanical rammer used to push the projectile (the first part of the round) into the breach was removed, once the Loader realised he could use the second part of the round, the Combustible Case Charge as the rammer.

The vehicles low ground clearance also proved a problem in very wet soft mud as the vehicle would sink and get banked by the mud under the hulls belly. Changes to the suspension to increase the ground clearance were made and to also cope with the additional weight from other design changes.

The FV4201 was accepted into British Army service in 1963 and named the Chieftain.

Chieftain Tank Firepower

Al-Khalid & Mk11 Chieftain Tank during TankFest

Al-Khalid & Mk11 Chieftain Tank during TankFest

The L11 main gun was specifically developed for the Chieftain. It wasn’t the first tank gun to have a bore calibre of 120mm, but was the first to have a calibre Length 55 making it the most powerful tank gun in NATO. The decision to make it so long was to increase the muzzle velocity (the speed measured of a projectile when it leaves the muzzle) when firing Armor Piercing Discarding Sabot rounds. The increased length meant the round had a great distance to travel in the barrel and allowed the explosive energy to build up behind it.

The higher m/v meant the AP rounds travelled faster, which increased their penetration capability and travelled further giving a greater range compared to other tank guns. The L11 was deemed so effective that it could penetrate any future Soviet Tank design for the foreseeable decades.

The L11 used a 2 part ammunition, though some consider it as 3 part. The first part is the projectile. These were commonly the L15 armour-piercing discarding sabot (APDS), L23A1 armour-piercing fin-stabilized discarding sabot (APFSDS), L31 high explosive squash head (HESH) and L34 Smoke round.

The second part is the charge. When firing APFSDS an orange cylindrical Combustible Case Charge was used. When firing HESH, a white satchel charge was used, which had less charge than a CCC. This was because HESH required a lower m/v so that the “pat” formed properly when striking an enemy vehicle.

The often considered third part was Vent Tube Electrical. Most tank guns worked like hand-held guns in that a mechanical pin struck the fuse at the bottom of the 1 part round to sit of the charge. The L11 did away with this and used an electrical charge from the VTE. The system was also considered more reliable.

The 2 part ammunition offered a number of advantages over 1 part ammunition was all encased in a brass shell. It was smaller, therefore easier to handle by the loader. It was safer to store, as HESH and the charges could be kept below the turret ring and the AP projectiles stored in the rear of the turret bustle. Its reduced size meant more rounds could be carried.

Chieftain Tank Mobility

Chieftain Tank TN12 Gearbox

Chieftain Tank TN12 Gearbox

The Chieftains L60 engine was designed and manufactured by Leyland. It was an opposed piston, two-stroke engine design. The L60 was capable of running on various fuels as required by NATO at the time. It was discovered during trials that to modify the engine’s fuel feed from diesel to another fuel could take up to 8 hours.

The NATO multi-fuelled concept was later abandoned by other NATO countries due to reliability issues, however it was left to late for the British to come up with a new engine following modifications to the tanks design to accommodate the L60.

Throughout the Chieftains service the engine earnt a reputation of problematic faults and reliability, though some crews found this not to be the case with all the engines. Various Marks (Mk) were introduced to rectify these problems as well increase the engines power for improved power to weight ratio:

Mark 1 to Mark 4 were prototype engines completed between 1959 and 1965
Mark 4A was the first production model built in January 1965 producing 585 bhp
Mark 4A2 had a new piston crown producing 650 bhp in November 1965
Mark 5A had a modified piston produced in April 1969
Mark 6A was produced in October 1970 with a two-stage air cleaner
Mark 7A was produced from October 1971 and had 720 bhp
Mark 8A had 750 bhp
Mark 9A various modifications including changes to the piston and fan drives
Mark 10A export version of the Mark 9A
Mark 11A to Mark 12A saw modifications to fix reliability issues
Mark 13A to Mark 14A were re-designations of earlier models in 1980

The Chieftains transmission (gearbox) was the TN12 by Self-Changing Gears ltd. The TN12 was operated by way of a kick pedal. The driver would change gears up by pressing the bottom with his heel and down gear by pressing the pedal top with his toes.

Chieftain Tank Marks

Chieftain Mark 1:

First production model, with No 11. Mk1 Commanders Cupola and Mk4A engine. Total of 39/40 built.

Sub-marks: Mark 1/1 modified exhaust, Mark 1/2 No 15. Mk1 Commanders Cupola, automotive upgrades and changes to headlights

Chieftain Mark 2:

New turret fitted with No. 15 Mk2 commanders cupola and Mark 4A2 engine. Sub Marks given when Tank Laser Sight and Muzzle Reference System installed

Chieftain Mark 3:

Mk 2 Chieftain with improvements to the suspension and installation of the Mark 6A L60 engine. Sub Marks given to when Tank Laser Sight and Muzzle Reference System installed.

Chieftain Mark 3/3:

Mk 3 with improved NBC system, Gunners sight, battery heating system and changes to the hull rear for installation of the Mark 7A engine at a later date. A number of other modifications made too

Chieftain Mark 5:

The Mk 5 was the finalised production Mark that incorporated all earlier Mark modifications. Firepower improvements included increased 120mm ammo storage to 64 rounds (including modified charge bins), new thermal sleeve commanders and gunners sighting equipment modified. NBC pack changed. Gearbox was strengthened and the L60 MArk 7A engine installed. The Mark 5 entered service in March 1972.

Additional Designations for Chieftain Mark 1 to 5:

L – Used when Tank Laser Sight had been retro-fitted to the tank
C – Used when the British Army Clansman Radio suite was added to the tank
MRS – Muzzle Reference System added to the tank

Chieftain Mark 5/2:

Re-designation of the Mk 5 when “L” and “MRS” were added.

The Totem Pole Conversion Programme

Started by the British Army to bring all previous Marks to the Mark 5 standard with the Mark 8A engine from 1975. It was broken down in to 3 elements:

X – Modification of the Gunners and Commander graticule to coincide with new ranging gun ammunition
Y – Modifications to the engine, brake, Gunners sight, Commanders firing switch and engine cut out as well as other small changes
Z – Modifications to the engine, improved NBC protection, oil-filled running gear assemblies and new gun clamp

Chieftain Mark 6:

Re-designation of the Mark 2 on completion of the Totem Pole conversion

Chieftain Mark 7:

Re-designation of the Mark 3 on completion of the Totem Pole conversion

Chieftain Mark 8:

Re-designation of the Mark 3/3 on completion of the Totem Pole conversion

Chieftain Mark 9:

Re-designation of the Mark 5 to 8 after conversion of ammo storage to APFSDS rounds

Chieftain Mark 10:

Re-designation of the Mark 9 once fitted with Stillbrew appliqué armor. Stillbrew was a non-reactive armor made up of rubber pads cross layered. When struck by HEAT ammunition they distort the path of the copper jet. It was moulded and applied across the front of the turret and around the drivers station.

Whilst Stillbrew was manufactured by Royal Ordnance Leeds, it was installed by the REME (Royal Electrical Mechanical Engineers) from 1986 onwards.

Chieftain Mark 11:

Re-designation of the Mark 10 when fitted with Thermal Observation and Gunnery System, aka TOGS. A total os 324 Chieftain were bought up to the Mk 11 standard.

Exported Chieftain Tank Marks

Chieftain Mark 3/3P:

British Army Mk 3/3 standard sold to Iran (P standards for Persia)

Chieftain Mark 4:

Developed for the Israeli Defence Force with the hope of Israeli licensed production, 2 prototypes were built and sent to Israeli for local testing and trials. The deal was cancelled by the UK in late 1969 due to objections from neighbouring Arab nations and both prototypes were returned to the UK. They are believed to have been sent to the USA for evaluation purposes.

Chieftain Mark 5P:

British Army Mk 5 standard sold to Iran in the early to mid-1970’s.

Chieftain Mark 5/2K:

British Army Mk 5/2 standard sold to Kuwait

FV4030 Program for Iran:

Mark 5/3P – A Mk 5P with enhanced mine protection, automatic gearbox, increased fuel capacity and modified suspension
FV4030/2 “Shir 1” – A stop gap design of the Chieftain (Mk 5?) with a new sloping rear to take a 1200bhp Rolls Royce engine and fitted with hydrogas suspension
FV4030/1 “Shir 2” – A reworked/modified hull (noted by its flat lower glacis) and new turret fitted with Chobham Composite armor, it was also fitted with hydrogas suspension. Despite being named “Shir 2” development had started prior to to the Shir 1.

Khalid:

Jordanian designation of a modified FV4030/2 “Shir 1”. It was fitted with a new multi-channel Commanders Sight and Fire Control System (some times referred to as “Al-Khalid”)

Mark 15 Qayd Al Ardh:

Produced for Oman. Possibly to the same standard as Mark 7

Chieftain Tank Models

A number of models  were developed for the export market based on the Chieftain, which in some cases had modified hulls and turrets so that Chobham Armor could be fitted, as well as improved engines and the latest Fire Control System technology. These were designated “Chieftain” followed by a number. In some cases the number represented the Horsepower the engine had been governed too.

Chieftain 800:

CV12 power pack, mock up Chobham armor.

Chieftain 900:

CV12 power pack, mock up Chobham armor, advanced optics, and night vision, fitted with Hydrostrut suspension.

Chieftain 1000:

Normal hull with mods, such as square final drive housings, rear exhaust box removed louvres fitted instead, large one piece rear decks, 1000bhp MTU pack coupled to Renk transmission. Only one built now lives at Elvington air museum. It was the Most powerful automotive chieftain built, when going flat-out and brakes applied it would stand on end sort of pose like the FV510 Warrior Infantry Fighting Vehicle.

Chieftain 2000:

Standard hull with CV12 pack and turret from the Chieftain 900.

Chieftain Tank Variants

The Chieftain was also built-in different variations, these included the FV4205 AVLB, the FV4204 ARV/ARRV (Armoured Recovery and Repair Vehicle), the Chieftain Mine Clearer, the Chieftain ARVE  (Armoured Vehicle Royal Engineers) the Chieftain Sabre-Twin 30 mm AA turret and the Weapon Carriers, where the Chieftain chassis was modified to mount air defence weapons (“Marksman” 2 x 35 mm cannon).

Chieftain Tank Operators

Kuwait 165 Mark 5/2K ordered with deliveries starting in May 1976.
Oman 27 delivered. 12 were used British Army Mark 7/2C and 15 new Mark 15. Still in service.
Iran – 707 Mark 3/3P and 85 Mk 5P delivered. In addition 71 ARV and AVLB were delivered. Still in service, an unknown number have been upgraded to the “Mobarez Tank”.
Iraq – Small number of Iranian Chieftains were captured in the Iran Iraq War.
Jordan – 278 Khalid ordered in 1979. Still in service.
Great Britain – Almost 1000 were built, from Mk 1 to Mk 5 and later all earlier Mk were bought up to the Mk 5 standard. The Chieftain Replacement Program eventually resulted in the Challenger 2 as its official replacement, finally being withdrawn from service around 1995 and its Combat support vehicles in the mid-2000’s.

Roughly 2265 Chieftains were built from 1965 to 1985.

Combat History

1980 to 88 Iran Iraq War – Operated by the Iranian Army, some were captured by Iraq from Iran.
1990 Iraq Invasion of Kuwait – Initially deployed by Kuwaiti Forces in defence of the invasion, 50 Chieftains joined the withdrawal of Kuwaiti Forces in to Saudi Arabia, only to return and participate in the Liberation of Kuwait in 1991.
1991 Gulf War – Other than those used by Kuwait, the British army only deployed Combat Support based Chieftains (such as AVRE) to aid their Challenger 1 Main Battle Tanks, whilst the Chieftain Mk11 remained stationed in West Germany.

Chieftain Tank Specifications

Firepower
Main Gun 120mm, calibre Length 55 Rifled
Secondary Weapons x1 coaxial 7.62mm MG, x1 7.62mm MG
Ammunition Storage x64 120mm, x6,000 7.62mm
Mobility
Engine Multi-fuel Leyland L60 6-cylinder series
Transmission TN12 semi-automatic
Top Road Speed 48 km/h
Road Range 400+ km
Fuel Capacity 950 Litres
Vertical Obstacle 0.91m
Water Capability 1.066m
Trench Crossing 3.14m
Gradient 60%
Side Slope 40%
Dimensions
Length Gun Forward 10.795m
Length Hull 7.518m
Width
3.504m (excluding search light)
Height 2.82m (top of the cupola)
Ground Clearance 0.508m
Weight 55,000kg aka 55 tonne combat (53 tonne empty)
Protection
NBC Protected Yes
Armor Type Steel
Active Protection Systems No
Crew
Commander Yes
Gunner Yes
Loader Yes
Driver Yes
Additional Crew
Troops Carried n/a

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