A Challenger 2 with a Mobile Camouflage System during an exercise (Picture: MOD).
By David Hambling, technology expert
Invented a century ago to break the deadlock of the First World War's trench warfare, the tank combined three key capabilities: mobility, protection, and firepower.
Mobility allowed it to cross the muddy terrain, trenches and barbed-wired of No-Man’s Land, armour made it invulnerable to the machine-gun fire that stopped infantry attacks, and the tank's weapons enabled it to destroy enemy positions.
A hundred years on, tanks still need the same three qualities, although the technology to provide them continues to improve.
Known as the Life Extension Program or LEP, the original aim was to prevent the tank from becoming obsolete, but it has expanded to include significant modifications.
Two bidders are in contention for the LEP, German tank-makers Rheinmetall and a team led by BAE Systems.
The winner will be announced later this year. Once that happens and the contract is awarded, we will get some idea of the real scope of changes and the upgraded version’s capability.
The LEP is likely to upgrade the Challenger 2’s firepower, replacing the existing rifled 120mm gun with a 120mm smoothbore weapon.
Britain was one of the last nations to hang on to the old rifled design, and the new gun will be more powerful, potentially more accurate and with greater range and hitting power.
The upgrade will not be simple though, because of the size of the smoothbore ammunition, which may require a completely new turret.
Another likely LEP modification is enhanced mobility. The existing tank has a 1200 horsepower (900 kw) engine giving a cross-country speed of over 40 km/h.
This could be replaced with a more modern 1600 horsepower unit giving a substantially greater performance.
The upgraded Challenger 2 will be in service until 2035 under current plans.
The US is also continuing to upgrade its existing tanks rather than starting from scratch.
There is also a new electronic jammer specifically designed to protect the tank from radio-controlled IEDs, a growing threat in counter-insurgency operations in Iraq and Afghanistan.
This use of electronics reflects a growing tendency to use technology rather than armour plate for protection.
In particular, the Israelis have claimed that their Trophy protective system on their Merkava tanks is highly effective against guided missiles.
This type of system has a radar with 360-degree coverage to detect incoming missiles and rocket-propelled grenades and intercepts them with short-range explosive charges before they can hit the tank. The US military is now adapting the Trophy for its own Abrams M1A2s.
Meanwhile, rather than making minor improvements, the Russians have come up with a completely new design, the T-14 Armata. Prototypes of this unusual tank took part in the May Day parade in 2015.
It has an unmanned turret with a powerful new 125mm gun (also capable of launching missiles) and an automatic loader, while the three-person crew are all housed in the hull.
This arrangement makes the turret smaller and keeps the crew away from the exploding ammunition in the case of a hit.
The Armata has a suite of active protection systems and new composite armour.
Western analysts were highly sceptical of whether the Armata would ever be more than a prototype, given the experimental nature of so much of its technology.
While the tank is now being produced, it is extremely expensive compared to the traditional, cheap, rugged tanks like the T-72.
Plans for 2,000 of them have been scaled back and the Russian army is unlikely to acquire more than a hundred Armatas.
Instead, they are likely to be relying – like their Western rivals – on upgrading their fleets of existing tanks.
Analysts have repeatedly claimed that the day of the tank is over, and that they are dinosaurs in the age of guided missiles.
However, tanks have proven invaluable in recent conflicts, and their combination of mobility, firepower and protection is still unmatched.
They will continue to be the masters of the battlefield, so long as they can continue to stay ahead of the threats.