The major fleet user of the J-type and the J/B was the General Post Office, who used them as Postal, Utility, Planners, and Radio Investigation vans. 6,147 J-types were bought by the GPO – approximately one in every eight of the vehicles built! The most obvious difference in the specification of these GPO J-types was the fitting of rubber front and rear wings, which required the fitting of the headlamps and sidelights to the cabside, rather than being mounted on castings on the wings as on standard vans. GPO vans had much improved locks for security, with Postal and Utility vans also having a rear door locking bar, which could be operated by the driver from inside his vehicle. Some GPO ‘J’ vans were also fitted with an opening driver’s windscreen. The GPO also tested a batch of diesel-powered J/Bs, one of which survived until recently on a farm near Stoke-on-Trent.