This blog provides images and information on interwar tank development by Vickers Armstrong Ltd. The photographs used have come from two works albums from Vickers Armstrong Ltd, held by the Beamish Museum and used here with permission. They also cover other vehicles including half tracks and wheeled transport.
This picture also appears on p63 of Ventham and Fletcher's Moving the Guns. It is the prototype 2 ton tractor, based on D5E1, the Artillery Observer's Vehicle, but without the high sided body. This prototype took part in the 1930 Wool trials. After performing well 14 vehicles were ordered (the Light Dragon) and delivered in 1931, when they were issued to 20 Battery of the 9th Field Brigade RA to replace their Birch Guns. The production veicle can be seen here.