"Troops man a mobile 12-pdr gun, mounted on the back of a lorry, at Fort Horsted, Chatham, 1 December 1940".
http://www.iwmcollections.org.uk/med...e/H_005865.jpg
I bought a print of this...it's an Albion 6 x 4 of around 1936-7 vintage. No idea yet which model but I have the census number somewhere ... just not near my filing cabinet!