The Vickers Main Battle Tank Mk. 4 later known as the Vickers Valiant was a main battle tank developed as a private venture by British company Vickers for export. Its development began in 1976 and ended in January 1984. Although the Valiant did not enter production, its development provided valuable experience in the production of an aluminium-hulled, Chobham-armoured tank in the 40 tonnes weight range. A further development of its turret was later used for the Vickers Mk. 7 MBT.

In August 1977, Vickers produced a design for a vehicle that incorporated Chobham composite armour protection within a battle weight of 43 tonnes.

This first prototype, designated the Vickers Main Battle Tank Mark 4, mounted the L7 105 mm rifled gun and, in 1978, underwent automotive tests with the Rolls-Royce CV12 TCA developing 1000 bhp and with the General Motors Detroit Diesel 12V-71T developing 915 bhp.

The prototype of the Mk. 4 was firstly exhibited at the British Army Equipment Exhibition in June 1980, along with a mock-up of a new universal turret fitted with a 120 mm L11 gun.

By the time of the British Army Equipment Exhibition in June 1982, the tank had undergone extensive testing with the new turret. The design of the Universal Turret was a radical change from the original and included installation of many state-of-the-art components. This quantum leap in turret evolution led to a decision to give the Mk. 4 a new identity, and it was renamed the " Valiant ". In early January 1983, the Valiant slipped off the low-loader of its tank transporter during transport at Larkhill and rolled onto its roof. The optics and the elevation gearbox were damaged and repaired within a week. It was then shipped to Lulworth ranges for trials on behalf of the ATDU (Armoured Trials and Development Unit).
From February to March 1983, the Valiant took part to the Floater '83 floating arms exhibition, touring the Middle East countries on the ferry Viking Venturer.
The Valiant went back to the Middle East in July and August of the same year where it was involved in desert trials in the United Arab Emirates along the British FV4030/4 Challenger 1 and the French AMX-40.

Its development was completed in January 1984. Although the tests of the Valiant in the Middle East indicated that the Valiant tank had excellent firepower and fire control components, the mobility characteristics were deficient, leading to the termination of its marketing effort in July 1985. Nevertheless, future automotive improvements were to improve the Valiant deficient mobility under the designation of Valiant 2.
The Universal Turret was fitted in 1985 to a German Leopard 2 hull to become the Vickers Mk. 7 main battle tank.

In 1989, the Valiant took part to the exercise Hellspot on Salisbury Plain with the purpose of trialling thermal sights. The fate of the hull, the first turret and the Universal Turret remains unknown to this date.

The fire control and gun stabilization system was an all-electric system developed by Marconi. This featured a built-in laser rangefinder and a brand-new solid-state ballistic computer to improve the chances of a first-round hit capability against static and moving targets as well as for supporting firing on the move. This system used the Marconi Radar SFCS 600 computer derived from the GCE 620 system installed on the Vickers Mk. 3 main battle tank with some improvements, known as the Marconi Radar systems Centaur 1 system.