The TN15 transmission was developed by Self-Changing Gears (SCG) Limited, recently taken over by David Brown Defence Equipment Limited for the Alvis Vehicles Scorpion CVR(T) family of tracked vehicles. Over 3,500 units have been completed. The basic TN15 is a crossdrive transmission matched to 149 kW (200 hp) petrol engines.

TheTN15 HD has been designed for diesel engines with a similar 149 kW (200 hp) output and is for the Alvis Scorpion and Stormer vehicles. The new T300 is a high-performance 224 kW (300 hp) transmission conceptually identical to the TN15 but is a new design using uprated components throughout.

The TN15 range of automatic crossdrive transmissions has been designed for independent mounting with drive transmitted through a resilient input coupling into a centrifugal clutch.

Planetary or epicyclic geartrains are used in the change speed sections to give seven ratios, with the transmission being fully bidirectional. Vehicle steering is achieved by the use of an integral Merritt-Brown triple-differential system. The two transmission outputs to the vehicle final drives are mounted at right angles to the transmission input.

The TN15 is now being offered with electro-hydraulic semi-automatic control systems or an electro hydraulic fully automatic control system as an option.

TN15 is installed in all members of the Alvis Vehicles Scorpion CVR(T) family. By mid-1999, over 3,500 TN15 transmissions had been completed.