In the 1970s, Rolls-Royce, subsequently the Perkins Engine Company Limited, signed a licence agreement with the now Allison Transmission of the USA, for final development and production of a version of the X-300 series automatic transmission for the Alvis Vehicles Warrior infantry combat vehicle then under development for the British Army.

Full-scale production of this transmission commenced in the UK in 1986 under the designation X-300-4B and since then, well over 1,100 units have been built for the Warrior for the British Army and more recently for the Desert Warrior (transmission designated the X-300-6) in service with Kuwait who ordered 254 vehicles with final deliveries taking place late in 1997.

It has been designed for installation in tracked armoured vehicles in the 20 to 36 tonne ranges and fitted with engines developing between 300 and 600 kW(402 to 804 hp).

The X-300-B is a fully automatic crossdrive transmission offering four forward and two reverse ranges driven through a torque converter and lock-up clutch.

Steering is infinitely variable with true pivot turn in neutral which is achieved with hydrostatically controlled double differentials.

Service and parking brakes are incorporated and are hydraulically applied with mechanical back-up. A generous live Power Take-Off (PTO) facility is provided together with a range of input torque converters to suit most engines. The X-300-4B is suitable for front or rear installation.

Following trials, the X-300-5 transmission was selected for all production versions of the Swedish Army's new Combat Vehicle 90 family of tracked vehicles with first production transmissions being shipped to Sweden in 1993.

Further development of the CV 90 as a private venture by Hagglunds Vehicle has resulted in the CV 9030N which is now in production for Norway. For this application the transmission is designated the X-300-5N and is coupled to a Scania DS 14 diesel engine developing 550 hp.

In production. Installed in Alvis Vehicles Warrior (UK), Alvis Vehicles Desert Warrior (Kuwait) Hagglunds Vehicles CV 9040 (Sweden) and CV 9030N (Norway). It is also installed in the private venture Alvis Vehicles Warrior 2000 infantry combat vehicle.