F.L. Douglas had previously worked for Universal Power Drives ( Unipower ), which in 1937 introduced a 4x4 timber tractor. He got his business up and running with timber tractor conversions of war-surplus AEC Matador 4x4 medium artillery tractors. They were equipped for the task with a powerful winch, fold-down lattice jib and, mounted at the rear of the chassis, a twin-spade land anchor. As war-surplus Matador stocks dried up, in 1950 the company progressed to more extensively modified developments based on civilian AEC models in production at the time.
With rough terrain proving the way to go, Douglas identified a market further down the payload scale for 4x4 and 6x6 conversions of mass-produced light trucks. The 6x6 variants had Douglas-produced Leyland Comet conversion was reportedly capable of climbing a 1-in-2.5 gradient with a 10-ton payload. Intriguingly, a normal-control Commer-based 1.5-ton payload 4x4, the Pathfinder, introduced in 1957, had the option of all-round Douglas developed unequal-length-wishbone independent suspension.
Alongside all-wheel-drive conversions, Douglas had by now introduced its first two- and four-wheel drive Tugmaster drawbar tractors for airfield and other applications. Tractive effort was from four tons upwards. A one-off special capable of moving 150 tons paved the way for the port and terminal tractors that became a mainstay product line. Terminal tractors benefited from a Douglas-designed elevating fifth wheel system for handling semi-trailers of virtually any coupling height. The first of this type, with a full-width cab and built in 1955, was for export to Venezuela. Douglas diversity was then extended to heavy 6x6 and 6x4 half-cab crane and excavator chassis and dump trucks. While dump trucks were a regular market for transfer cases and lightweight higharticulation bogies incorporating a central trunnion suspension arrangement that allowed each wheel nine inches of articulation before losing traction. Donor chassis were primarily Luton-built Commer forward- and normal-control models, and to a lesser extent shortbonneted Leyland Comets and Austin Loadstars — and even Bedfords. ("Trucking Magazine")