This vehicle was officially known as the Lorry, 4-Ton, 6-WH, Crane, Mark VII with the sub designation Bay City Crane, 4-ton, 6 x 6, 201 wb. As this allready suggests is, that it was a 201" wheelbase 4-ton 6x6 Diamond T with the Bay City Crane 4½-Ton capacity. Another designation was the Lorry Type Derrick.

The text states that these vehicles were primarily used by te RCE (Royal Canadian Engineers). It was intended for general lifting work required for the building of bridges. Evidence was found that it also was used to lift pontoons for treadway bridges. It's role was very broad as you can read in the page from the Vehicle data book for the Canadian Army Overseas. It's overall dimensions can be taken from the same page.

Shoulder patch of the R.C.E.

Left and right sides of this vehicle from the Manual,

Front and rear view of the same vehicle.

Right side of the crane itself.

Maximum loads of the crane were 4480 lbs. at an 8ft. radius and 2240 lbs. at a radius of 13 ft.

The Canadian Technical Manual states: "The Derrick is designed to assist engineers to perform bridge building operations, for the moving of heavy timbers and general lifting of heavy material etc." The body is of steel construction and in the form of a cab, is mounted on a turntable which is directly connected to the rear of chassis frame. It encloses the engine and operating levers for the crane and provides seating accommodation for the operator. The rear of this* cab has semi-circular sliding doors for protection against adverse weather conditions. Upper and lower windows at the front on the right side provide visibility for the operator, likewise a side window.

The crane consists of a boom with front and rear winches and necessary operating and control levers. This is mounted on a turntable and powered by a gasoline engine. This is a six cylinder water cooled gasoline engine equipped with self starter, and supplies power for operation of the crane. When the crane is not in use the hook must be inserted into an eye provided on the crane and cable slack taken up by looping cables over hook attached to neck of the crane.

Above the left and right side of the Hercules JXC engine that provides the power for the crane. On the right you can see the engine mounted in place in the crane cab. Below are a few drawings from the manual that shows the general layout of the crane and the rotating base on the chassis of the crane on the Diamond T.

Engine specifications:

Type	:	"L" Head
Number of Cylinders	:	6
Bore	:	3-3/4"
Stroke	:	4-1/4"
Piston Displacement	:	282 cu. in.
Compression Ratio	;	5.35:1
Horsepower - Max. Brake	;	72.5 at 2600 R.P.M.
S.A.E. Horsepower	;	33.75
Maximum Torque	;	176 ft. lbs. at 1000 R.P.M.

Two extra pictures of the Diamond T with the Bay City Crane.

Bibliography:

- Drive to Victory - A Catalogue of Canadian Army Softskin Vehicles by C.M. Law 2016
- Vehicle Data Book Canadian Army Overseas 1944
- Lorry Type "Derrick" Manual WM-3919 April 1943
- Bay City Crane Manual WM-3890 June 1943