The TN26 transmission was developed specifically for the Royal Ordnance Combat Engineer Tractor in service with India, Singapore and the UK.

It is a specialist in-line unit with torque converter coupling and four ratios in both forward and reverse. The directional selections give a high-ratio, high-output speed operation for road running and a low-ratio, high-torque operation for working operations such as bulldozing and digging. In the road running selection the torque converter is locked out in third and fourth gears by a hydraulically actuated clutch.

The torque converter is a three-element unit with a stall torque ratio of 3.1:1 and a diameter of 330 mm. The unit is driven from the engine via a step-up transfer box giving a maximum speed to the converter of 3,550 rpm.

The transmission is manually operated using selector switches for selection of the ratio gears and direction change. The unit can be fully automatic.

In the event of vehicle electrical system failure or malfunction, two manual override gears can be achieved by mechanical actuation of the hydraulic valves/The ratios selected are forward and second, for example high second, or reverse and third, for example low third. Selection is by means of a lever on the hydraulic valve block housing.

The transmission output is taken to a separate steer unit. In the particular vehicle for which the TN26 was designed, controlled differential steer is used for road driving and skid steer for most effective bulldozing and similar work.

The TN26 transmissions was originally designed and built by Self-Changing Gears which then became Alvis Transmissions. This company was sold to David Brown Defence Equipment in early 1998.

In production. Installed in the Royal Ordnance Combat Engineer Tractor (CET) in service with India, Singapore and the UK. By mid-1999, well over 200 TN26 transmissions had been manufactured.