The FV4601 MBT-80 was a British experimental third-generation

main battle tank A main battle tank (MBT), also known as a battle tank or universal tank, is a tank that fills the role of armor-protected direct fire and maneuver in many modern armies. Cold War-era development of more powerful engines, better suspension sys ...

, designed in the late 1970s to replace the

Chieftain A tribal chief or chieftain is the leader of a tribal society or chiefdom. Tribe The concept of tribe is a broadly applied concept, based on tribal concepts of societies of western Afroeurasia. Tribal societies are sometimes categorized a ...

tank. It was eventually (and later controversially) cancelled in favour of the

Challenger 1 The FV4030/4 Challenger 1 is a British main battle tank (MBT) used by the British Army from 1983 to 2001, when it was superseded by the Challenger 2. It is also currently used by the Royal Jordanian Army as its main battle tank, after heavy ...

, itself an evolution of the Chieftain design.

History

By the early 1970s, there was a great disparity in the number of tanks being fielded by

NATO The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two N ...

and the

Warsaw Pact The Warsaw Pact (WP) or Treaty of Warsaw, formally the Treaty of Friendship, Cooperation and Mutual Assistance, was a collective defense treaty signed in Warsaw, Poland, between the Soviet Union and seven other Eastern Bloc socialist republi ...

in Europe. The

US Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...

fielded the M60 which had been designed to deal with the 100 mm gun of the

T-55 The T-54 and T-55 tanks are a series of Soviet main battle tanks introduced in the years following the Second World War. The first T-54 prototype was completed at Nizhny Tagil by the end of 1945.Steven Zaloga, T-54 and T-55 Main Battle Tank ...

, but could not withstand the 115 mm gun being fielded on the

T-62 The T-62 is a Soviet main battle tank that was first introduced in 1961. As a further development of the T-55 series, the T-62 retained many similar design elements of its predecessor including low profile and thick turret armour. In contras ...

, let alone the newer 125 mm model of the

T-64 The T-64 is a Soviet tank manufactured in Kharkiv, and designed by Kharkiv Morozov Machine Building Design Bureau. The tank was introduced in the early 1960s. It was a more advanced counterpart to the T-62: the T-64 served in tank divisions, whil ...

and

T-72 The T-72 is a family of Soviet/Russian main battle tanks that entered production in 1969. The T-72 was a development of the T-64, which was troubled by high costs and its reliance on immature developmental technology. About 25,000 T-72 tanks h ...

. The same-era West German design, the

Leopard 1 The Leopard 1 (also styled Leopard I, before the Leopard 2 simply known as Leopard) is a main battle tank designed and produced by Porsche in West Germany that first entered service in 1965. Developed in an era when HEAT warheads were though ...

, was very lightly armoured based on the conclusion that heavy armour had little purpose in an era of

high-explosive anti-tank High-explosive anti-tank (HEAT) is the effect of a shaped charge explosive that uses the Munroe effect to penetrate heavy armor. The warhead functions by having an explosive charge collapse a metal liner inside the warhead into a high-velocity ...

(HEAT) weapons of rapidly improving performance. The concept was to give the tank high manoeuvrability to allow it to outmanoeuvre the slower-moving Soviet tanks and early generation missiles that were difficult to use against moving targets. This decision proved unwise as the number of Soviet tanks grew and the idea of outmanoeuvring their massed numbers seemed unworkable, while second-generation missiles made aiming at moving targets easy. In 1963 the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

and

West Germany West Germany is the colloquial term used to indicate the Federal Republic of Germany (FRG; german: Bundesrepublik Deutschland , BRD) between its formation on 23 May 1949 and the German reunification through the accession of East Germany on 3 ...

started a joint project to develop a new tank to be used by both forces, the

MBT-70 The MBT-70 (German: ''KPz 70 or KpfPz 70'') was an American– West German joint project to develop a new main battle tank during the 1960s. The MBT-70 was developed by the United States and West Germany in the context of the Cold War, intende ...

. This combined the manoeuvrability of the Leopard with improved armour that would offer better protection against HEAT rounds while adding a new missile-firing gun able to engage Soviet tanks at very long range. By the late 1960s, the MBT-70 project had repeatedly overrun its development budget and the US Congress eventually cancelled it. By this point, the only western tank able to go head to head with the latest Soviet types was the

British Army The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. , the British Army comprises 79,380 regular full-time personnel, 4,090 Gurkha ...

, introduced to service in 1967. The Chieftain had heavy armour designed specifically to defeat the 115 mm, and mounted a 120 mm gun, among the most powerful in the world, able to defeat even the latest Soviet armour. When the 125 mm gun was introduced by the Soviets, the "Stillbrew armour" package was added to keep the tank competitive. However, the Chieftain had a number of problems due to its rather poor engine and outdated suspension, both of which conspired to make cross-country performance rather limited. The Germans were still looking for a tank to replace their now outdated Leopards, as well as the many

M48 Patton The M48 Patton is an American first-generation main battle tank (MBT) introduced in February 1952, being designated as the 90mm Gun Tank: M48. It was designed as a replacement for the M26 Pershing, M4 Sherman, M46 and M47 Patton tanks, and w ...

tanks they still had in service. The UK was looking for a more manoeuvrable design. A new joint program was formed between the UK and West Germany to develop a Future Main Battle Tank (FMBT). This was expected to replace the Chieftain tanks starting in the 1980s, as well as the older West German tanks. In 1977, Frederick Mulley, then

Secretary of State for Defence The secretary of state for defence, also referred to as the defence secretary, is a secretary of state in the Government of the United Kingdom, with overall responsibility for the business of the Ministry of Defence. The incumbent is a membe ...

, announced that, while both countries had agreed on the specifications of the joint tank, the replacement timetables diverged to such a degree that collaboration was not practicable at that time. The cancellation of the MBT-70 had led the US to begin the development of its own design, the XM1. Prototypes arrived in 1976 with production slated for the late 1970s. Using the UK's new Chobham armour, it was emerging as a potent design. When carefully examined by the British Army, a number of issues became apparent. Notable was the 105 mm gun, which did not have the power to defeat the latest Soviet designs at long range, the preferred action for British tankers. Moreover, the armour package had been designed to defeat either the 115 mm firing

armour-piercing fin-stabilized discarding sabot Armour-piercing fin-stabilized discarding sabot (APFSDS), long dart penetrator, or simply dart ammunition, is a type of kinetic energy penetrator ammunition used to attack modern vehicle armour. As an armament for main battle tanks, it succeeds ...

(APFSDS) or 125 mm firing

(HEAT) rounds, but could not stop the 125 mm firing APFSDS at reasonable range. Despite this, the desire to replace the Chieftain with a more mobile design remained, and there was some consideration given to importing XM1 hulls and turrets and then fitting them out with British-made components such as engine, transmission, and the 120 mm gun from the Chieftain on a domestic production line to produce a new tank. Reports on the XM1 were not favourable though. Ultimately the UK instead officially began development of the MBT-80 in September 1978. This new project would build on work already carried out by the Military Vehicles and Engineering Establishment (MVEE) as far back as 1968, when they had produced a tank prototype with an external (unmanned)

turret Turret may refer to: * Turret (architecture), a small tower that projects above the wall of a building * Gun turret, a mechanism of a projectile-firing weapon * Objective turret, an indexable holder of multiple lenses in an optical microscope * M ...

. This was followed in 1978 by another tank prototype fitted with

Chobham armour Chobham armour is the informal name of a composite armour developed in the 1960s at the British tank research centre on Chobham Common, Surrey. The name has since become the common generic term for composite ceramic vehicle armour. Other name ...

. This later prototype was based on the Chieftain design, and had the designation FV4211.

Design

The MBT-80 was designed to counter all current and future armoured threats from the

Eastern Bloc The Eastern Bloc, also known as the Communist Bloc and the Soviet Bloc, was the group of socialist states of Central and Eastern Europe, East Asia, Southeast Asia, Africa, and Latin America under the influence of the Soviet Union that existed du ...

, combining a rifled gun, advanced composite armour and increased mobility onto one platform. Other design features included the use of a David Brown Gear Industries TN-38 transmission, a Sperry/Vickers stabilised panoramic sight for use by the tank commander, and an advanced

vetronics Vetronics, a portmanteau of vehicle and electronics, is a technological designation used extensively in the military domain. The term also has limited usage in other contexts and in company branding, particularly in the veterinary and medical doma ...

suite incorporating

Ferranti F100-L The Ferranti F100-L was a 16-bit microprocessor family announced by Ferranti in 1976 which entered production in 1977. It was the first microprocessor designed in Europe, and among the first 16-bit single-chip CPUs. It was designed with military us ...

microprocessors. The MBT-80 would have also been the first operational British tank to have a crew compartment with a full environmental system; i.e. able to provide both

heating, ventilation, and air conditioning Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality ...

for the crew.

Armament

The main armament of the MBT-80 was to be a 120 mm rifled gun, the EXP-28M1, similar in some respects to the main guns found on the

and later the

and

Challenger 2 The FV4034 Challenger 2 (MOD designation "CR2") is a third generation British main battle tank (MBT) in service with the armies of the United Kingdom and Oman. It was designed and built by the British company Vickers Defence Systems (now known ...

main battle tanks, but a new design of its own. It was an advanced development of the Royal Ordnance L11A5 tank gun, designed by the

Royal Armament Research and Development Establishment Royal may refer to: People * Royal (name), a list of people with either the surname or given name * A member of a royal family Places United States * Royal, Arkansas, an unincorporated community * Royal, Illinois, a village * Royal, Iowa, a c ...

(RARDE), with a split-block breach mechanism. It was one of the first tank guns to use an Electro Slag Refined Steel (ESRS) barrel. This new barrel was intended to greatly increase the fatigue life of British 120mm tank guns. The technology had been cleared for use by new tank gun designs in 1976. The

fire-control system A fire-control system (FCS) is a number of components working together, usually a gun data computer, a director, and radar, which is designed to assist a ranged weapon system to target, track, and hit a target. It performs the same task as a ...

(FCS) would access and process relevant target, environment, and gun status data from various internal and external sensors including laser rangefinders and thermal imagers, to help the main gun hit targets accurately and consistently under more adverse conditions: "First shot, first kill". Major components of the FCS included the Fire Control Computer which was the 'brains' of the FCS, the Gun Control Equipment, and the STAMPLAR sight (see below), all of which were connected together by a fully digital databus. The FCS was also designed with

built-in self-test A built-in self-test (BIST) or built-in test (BIT) is a mechanism that permits a machine to test itself. Engineers design BISTs to meet requirements such as: *high reliability *lower repair cycle times or constraints such as: *limited technic ...

diagnostics. The commander and gunner had duplicate turret/main gun controls, so either of them could aim and fire the main gun. Ammunition for the EXP-28M1 would have included

(APFSDS, APDS-T),

(HEAT),

high-explosive squash head High explosive squash head (HESH) in British terminology, or high explosive plastic/plasticized (HEP) in American terminology, is a type of explosive projectile which uses a plastic explosive that conforms to the surface of a target before detona ...

(HESH), and smoke-white phosphorus rounds. Secondary armament would have included a 7.62 mm L37A1 General Purpose Machine Gun mounted on the commander's

cupola In architecture, a cupola () is a relatively small, most often dome-like, tall structure on top of a building. Often used to provide a lookout or to admit light and air, it usually crowns a larger roof or dome. The word derives, via Italian, f ...

, which could be aimed and fired from within the tank. L2A1 "ball" and L5A1 tracer rounds would have been among the ammunition available for this weapon.

Protection

The MBT-80 was going to be protected mainly by the recently developed

, first fielded on the American M1 Abrams. The armour would have provided greater resistance against high explosive anti-tank (HEAT) rounds and kinetic energy penetrators. Thanks to the use of Chobham armour, it was anticipated that much greater use could be made of high grade aluminium alloy in the construction of the

hull Hull may refer to: Structures * Chassis, of an armored fighting vehicle * Fuselage, of an aircraft * Hull (botany), the outer covering of seeds * Hull (watercraft), the body or frame of a ship * Submarine hull Mathematics * Affine hull, in affi ...

(the turret was steel) than in prior tank designs, helping to keep down the overall weight of the tank and therefore improve mobility and associated logistics, not to mention transportation of the tank to where it would be needed. The tank would also have had among other protection features a full

active Active may refer to: Music * ''Active'' (album), a 1992 album by Casiopea * Active Records, a record label Ships * ''Active'' (ship), several commercial ships by that name * HMS ''Active'', the name of various ships of the British Royal ...

NBC defences, something that was becoming more common on military vehicles being designed and/or introduced in the late 1970s and early 1980s. This included both advanced NBC sensors and radiation/

electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrost ...

(including

electromagnetic pulse An electromagnetic pulse (EMP), also a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. Depending upon the source, the origin of an EMP can be natural or artificial, and can occur as an electromagnetic f ...

) shielding to help protect the crew and vehicle systems. An extensive

electronic warfare Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponent ...

system including a dedicated

electronic counter-countermeasure Electronic counter-countermeasures (ECCM) is a part of electronic warfare which includes a variety of practices which attempt to reduce or eliminate the effect of electronic countermeasures (ECM) on electronic sensors aboard vehicles, ships and ai ...

ability was also to be included. This system would have incorporated various

countermeasure A countermeasure is a measure or action taken to counter or offset another one. As a general concept, it implies precision and is any technological or tactical solution or system designed to prevent an undesirable outcome in the process. The fi ...

s against such threats as a

rocket-propelled grenade A rocket-propelled grenade (RPG) is a shoulder-fired missile weapon that launches rockets equipped with an explosive warhead. Most RPGs can be carried by an individual soldier, and are frequently used as anti-tank weapons. These warheads a ...

(RPG) or

anti-tank guided missile An anti-tank guided missile (ATGM), anti-tank missile, anti-tank guided weapon (ATGW) or anti-armor guided weapon is a guided missile primarily designed to hit and destroy heavily armored military vehicles. ATGMs range in size from shoulder ...

(ATGM), 1st through 3rd generation. As a thermal signature management measure, the exhaust gases from the

Rolls-Royce Rolls-Royce (always hyphenated) may refer to: * Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct Automobiles * Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...

CV12 TCA Condor engine would have been mixed with cooling air before being discharged outside the tank. This feature was also used on the Vickers Valiant MBT. Mounted on the sides of the turret would have been two L8A1 six-barrelled 66 mm

smoke Smoke is a suspension of airborne particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-produc ...

grenade dischargers, the same British system was used as the

M250 grenade launcher The M250 consists of two six-barrel 66-millimeter grenade launchers (the British No. 19 Mk 2 design)http://www.pica.army.mil/pmccs/d5forceapplication/...1Grenades/M82.htm used on the M1 Abrams The M1 Abrams is a List of main battle tanks by ...

s found on early models of the

M1 Abrams The M1 Abrams is a third-generation American main battle tank designed by Chrysler Defense (now General Dynamics Land Systems) and named for General Creighton Abrams. Conceived for modern armored ground warfare and now one of the heaviest t ...

Mobility

The MBT-80 was to have a longer range, more mobility, and greater speed than prior tanks. Two options were considered; the Honeywell AGT1500 gas turbine engine used by the United States's prototype XM1 Abrams tank, producing 1,500 hp, and a modified,

turbocharged In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pr ...

version of the Rolls-Royce CV12 diesel engine, also producing 1,500 hp. The CV12 was eventually picked, mainly because the AGT1500 would need substantial modification of the tank to suit the transmission that came with the engine, which had been specially designed for the XM1. The higher fuel use of the gas turbine engine was also a factor in choosing the diesel engine. The CV12 was expected to be produced at Rolls-Royce's Shrewsbury plant.

Sensors

Known sensors included: * Sperry/Vickers stabilised sight for tank commander - Daytime sight only with ×1–10 magnification. * PANTILI (Panoramic, Thermal Imager, Laser Integrated Sight) - 360 degree rotating thermal imager fitted with a ()

laser rangefinder A laser rangefinder, also known as a laser telemeter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in ...

. Accessible to both commander & gunner. Similar in concept to the ''hunter-killer'' sight found on the later Challenger 2 tank. * Two axis stabilised monocular gunners sight incorporating a laser rangefinder and muzzle reference system, magnification ×2–3 and ×10. Backup telescope with ×8 magnification also provided. * Driver's thermal imager - possibly the Barr & Stroud IR18 TVFS but this is unconfirmed. The IR18 was later used as part of the Challenger 1's TOGS (Thermal Observation and Gunnery Sight) system. * STAMPLAR (Sight, Thermal, Armoured, Periscope, LAser Rangefinder) - Part of the fire control system. Directly tied into the Fire Control Computer via a digital databus. * Roof-mounted infra-red detector - Part of the NBC defence suite, it could detect airborne

chemical weapon A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as a ...

agents and radioactive

nuclear fallout Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioac ...

. Later available as an option on the ''Chieftain 900'' tank.

Versions and variants

Among the projected vehicles based on the MBT-80 chassis were a

self-propelled anti-aircraft weapon An anti-aircraft vehicle, also known as a self-propelled anti-aircraft gun (SPAAG) or self-propelled air defense system (SPAD), is a mobile vehicle with a dedicated anti-aircraft capability. Specific weapon systems used include machine guns, ...

(gun: SPAAG) using the turret of the

Flakpanzer Gepard The ''Flugabwehrkanonenpanzer Gepard'' ("anti-aircraft-gun tank 'Cheetah, better known as the Flakpanzer Gepard) is an all-weather-capable German self-propelled anti-aircraft gun (SPAAG). It was developed in the 1960s, fielded in the 1970s, a ...

, an armoured vehicle-launched bridge (AVLB), and an

armoured recovery vehicle An armoured recovery vehicle (ARV) is typically a powerful tank or armoured personnel carrier (APC) chassis modified for use during combat for military vehicle recovery (towing) or repair of battle-damaged, stuck, and/or inoperable armoured ...

(ARV). None of these had progressed beyond the concept stage at the time of the programme's unexpected cancellation.

Cancellation

In the aftermath of the

Iranian Revolution The Iranian Revolution ( fa, انقلاب ایران, Enqelâb-e Irân, ), also known as the Islamic Revolution ( fa, انقلاب اسلامی, Enqelâb-e Eslâmī), was a series of events that culminated in the overthrow of the Pahlavi dyna ...

, all orders for weapons from the United Kingdom were cancelled, including those for Shir 2 tanks. The British defence industry was heavily reliant on the Iranian market, forcing the government to cut the number of workers at ROF Leeds. At this same time, the government was looking into how they could still retain the skill and capacity at Leeds that would be needed to produce the next generation of main battle tanks. Despite attempts to put the tank into production as quickly as possible, it would not be until the mid-1980s that the MBT-80 would be ready for production even if development was drastically accelerated. In addition, there were increasing worries that Soviet tank technology was advancing at such a rate that new designs, such as the

T-80 The T-80 is a main battle tank (MBT) that was designed and manufactured in the former Soviet Union and manufactured in Russia. The T-80 is based on the T-64, while incorporating features from the later T-72. The chief designer of the T-80 was S ...

, reportedly about to enter service would obsolete extant front line British MBTs far sooner than predicted formerly. Ultimately, the entire programme was cancelled in favour of the

Challenger Challenger, Challengers, or The Challengers may refer to: Entertainment Comics and manga * Challenger (character), comic book character * ''Challengers'' (manga), manga by Hinako Takanaga Film and TV * ''The Challengers'' (TV series), a 197 ...

, which had been developed from the Shir 2 as a private venture, and would be in theory available for service by 1983 to replace the Chieftain tanks instead. With its adoption as an official programme, the Challenger was also known for a time as the ''MBT-85''. However, various research elements of the MBT-80 programme were continued to develop and mature advanced technology for the next generation of British MBTs to enter service in the early 1990s, the design of which was to be provided by the new ''MBT-95'' programme, launched in late 1982. In the event though, the MBT-95 was superseded by the Challenger 2 programme in 1987 in part due to financial and political considerations and partly due to the unexpectedly poor performance of the original Challenger in early trials, exercises and the like which seemed to indicate an urgent need for a replacement tank in the near term, and not just to replace the remaining Chieftains as originally planned. However, the Challenger 2 was not officially chosen as the

's new tank until late 1991, by which time the Challenger 1's problems had been resolved, with it having racked up an excellent operational record in the

Gulf War The Gulf War was a 1990–1991 armed campaign waged by a 35-country military coalition in response to the Iraqi invasion of Kuwait. Spearheaded by the United States, the coalition's efforts against Iraq were carried out in two key phases: ...

. The MBT-80 was planned for development to be completed in 1987 and production by 1989. By 1989 the Challenger tank at the same point in time, despite having been in production for nearly seven years and officially in service for over four of those, was widely considered to be still not fully operational.

Surviving vehicles

Two test rigs were built to test the various systems that would be used in the planned MBT-80. The first, Automotive Test Rig 1 (ATR1), had a hull assembled from

Shir 2 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 r ...

prototypes derived from the

, removable blocks of armour that either contained Chobham or steel designed to imitate it, and a dummy tank gun. It could also move under its own propulsion. ATR1 fell into the hands of a private collector but is currently in bad condition. The second rig, ATR2, was designed to test the ability to weld

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

and

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...

tank hulls together to reduce weight. It also had a different turret design from the ATR1 and possesses advanced sights that were state-of-the-art at the time of construction. ATR2 is currently displayed in the Vehicle Conservation Centre of the

Bovington Tank Museum The Tank Museum (previously The Bovington Tank Museum) is a collection of armoured fighting vehicles at Bovington Camp in Dorset, South West England. It is about north of the village of Wool and west of the major port of Poole. The collecti ...

Dorset Dorset ( ; archaically: Dorsetshire , ) is a county in South West England on the English Channel coast. The ceremonial county comprises the unitary authority areas of Bournemouth, Christchurch and Poole and Dorset. Covering an area of , ...

Notes

References

External links

Main MBT-80 thread over at the Secret Projects Forum
{{ModernUKAFVsNav, style=wide Main battle tanks of the United Kingdom Main battle tanks of the Cold War Abandoned military projects of the United Kingdom History of science and technology in the United Kingdom History of the tank Trial and research tanks of the United Kingdom