As a replacement for the Chieftain, the Challenger arrived almost as an accident. Although it was planned already in the 1970s, the Export versions of the Chieftain really gave the impetus to develop the new main battle tank, not in all directions as the main armament and protection of the latter was unsurpassed at the time, but in the field of mobility, which was indeed its main critic.
Iran noticeably, prior to the 1979 revolution acquired the Chieftain and was quite happy with it, but ordered a mobility improvement which gave birth to the 4030/3 Shir 2 by Military Vehicles and Engineering Establishment (MVEE) near Chobham in Surrey.
It also came with a brand new armor package which was even far superior. After the fall of the Shah and the order cancellation, all this development work was passed into the Cheviot, later known in the final phase, the Challenger, in remembrance of the ww2, 17-pdr armed first version. The Challenger was replaced in 1990 by the all-improved Challenger 2, and both tanks were largely battle-tested in Iraq and Afghanistan.
Development: From the Shir to the Challenger.
In 1977, an Iranian order for an improved version of the Chieftain came out. After the MVEE created the Chieftain Mark 5(P), giving birth to three prototypes, also known as the FV4030/1, the FV4030/2 Shir (Lion) 1 (in service with the Jordanian Army), and later the 4030/3 Shir 2. The Shir 1 (ordered by Jordan) possessed an improved running gear that will turn to be the one designed for the Challenger 1. It was also a transition vehicle to the Shir 2.
The latter was canceled after the fall of the Shah in 1979, but the project came out as a new design after reworking at ROF Leeds. The chassis front half came from the Chieftain, the running gear and rear section from the 4030/2 Chassis Shir 1. The roomier compartment allowed to fit a much more powerful Rolls-Royce CV12 engine producing 1200 bhp at 2,300 rpm.
Among other modifications proper to the Shir 2 were the removal of the searchlight (left turret), refitting of the storage baskets, removal of the driver’s hatch water channel, the glacis plate light clusters were modified and the sight housing on the commander’s cupola was enlarged. The final design was sanctioned at the Royal Ordnance Factories (ROF). After being re-christened Cheviot and then Challenger, the new MBT was accepted and entered service with the British Army in 1983. Production ceased in 1989.
The Challenger I was kept in service until 2001 (ported at the Mk.4 standard), when it was replaced by the Challenger 2, which only shared 5% of common parts with the Challenger 1.
Design of the Challenger
The crew comprised the driver, seated in a well reclined position, located in the center of the very shallow hull, forward of the turret ring, with its own forward-folding hatch fitted with three observation periscopes and central sight that can be swapped for a Pilkington Optronics Badger passive periscope for night driving, while the three other members of the crew are located in the turret.
The gunner is installed in the front-right, with the commander right behind while the loader is seated on the left, with ready round ammunitions and access to the turret bustle rounds storages. The commander has an excellent peripheral view thanks to the nine vision blocks of its No 32 cupola. He had a day sight that could be replaced quickly by a Rank Pullin image intensification swap sight. This provided excellent day/night magnification and there is a cupola ring for holding an optional LMG mount.
Hunter-Killer mode is standard thanks to the TOGS system (Thermal Observation and Gunnery Sight) by separating the target output. The latter was manufactured by Barr & Stroud and Avimo. The gunner is in charge of the main targeting sight, fitted with IR day/night magnification and Nd:YAG laser FCS which range is 11,000 yards (10,060 m).
Observed accuracy is in the range of 10 m for 90% of shots at 10,000 m. The gunner also has a backup, the emergency No 87 periscopic sight normally hidden under armor and collimated with the gun. The loader have a roof-mounted x1 periscope swivel-mounted forward of his two-piece hatch cover.
The turret is almost perpendicular in shape, with a well-sloped front and low profile walls. Additional storage is provided at the back and rear sides. There are provisions at the back of the hull for extra fuel drums. The crew is protected by a collective NBC with a pressured compartment and slight overpressure system. There are automatic fire extinguisher systems in the turret and engine compartments.
The ROF and MVEE team resulted in other modifications. The level of protection was raised even further with the adoption of the new Chobham armour, which composition remains highly classified (it is shared by the Abrams that inaugurated it). Speculations about its composition remains uncertain, but levels of soft and hard steel, kevlar, carbon, rubber and possible others polymers are sandwiched with Ceramic, which is the most important material.
Its hardness and extreme heat resistance indeed helps defeat shaped charge jets (HEAT rounds), but also to shatter kinetic energy penetrators (KE-penetrators) as being abrasive.
The shattering characteristics also creates extreme asymmetric pressures that disturbs the geometry of the jet, making it less effective. The interaction of ceramic with the metal jet also was compared to the effect of the explosive reactive armour. Both the Chobham and Chobham 2 (on the Challenger 2) were largely proven in combat, in the 1991 and 2003 gulf wars, Afghanistan and Iraq, proving both the Challenger and Abrams nearly impossible to destroy, or at least helping the crew survive many hits. This armor is mostly fitted on the turret, which shape is quite different than the Challenger’s initial own RHA conception. But elements are found on the upper hull sides and glacis.
The engine compartment is home of the new Perkins Condor CV12 26 liter diesel 1,200 hp (895 kW) fitted with two Garrett-AiResearch turbochargers, to compare to the previous Chieftain’s initial Leyland L60 multifuel 2-stroke opposed-piston giving 750 hp (560 kW) 6 Cylinders, 19 liters.
The latter was 55 tonnes, while the Challenger is 62 tonnes, but the raw power almost doubled, allowing a much better power-to-weight ratio. Compared to other MBT which engine output is 1500 hp, but the powerplant can be changed in 45 minutes in the field and also have an auxiliary unit (APU).
The engine is driven by a David Brown Defence Equipment Limited TN37 transmission. The torque converter is a Borg-Warner with lock-up clutch. The gearbox have four forward and three reverse gears, and steering is a Commercial Hydraulics STN37 double differential with hydrostatic and infinitely variable control.
The powerplant was only part of the package, which came also with a brand new set of hydropneumatic (Hydrogas) suspension units designed by MVEE in conjunction with Air-Log Limited, and assembled by Vickers. The tracks are travelling with six aluminium roadwheels and two return rollers per sides.
This active system is much more advanced than the old Horstmann system used on the Chieftain and Centurion, allowing for greater weight and higher speed, at 56 kilometres per hour (35 mph) instead of 48 km/h (30 mph) on flat, but for the Chieftain this figure fall far beyond cross country which the hydrogas suspensions allowed to maintain an excellent off road cruise speed.