Diesel locomotive
Diesel locomotives offer significant operating advantages over steam locomotives. They can safely be operated by one person, making them ideal for switching/shunting duties in yards (although for safety reasons many main-line diesel locomotives continue to have 2-man crews: an engineer and a conductor/switchman) and the operating environment is much more attractive, being quieter, fully weatherproof and without the dirt and heat that is an inevitable part of operating a steam locomotive. Diesel locomotives can be worked in multiple with a single crew controlling multiple locomotives in a single train — something not practical with steam locomotives. This brought greater efficiencies to the operator, as individual locomotives could be relatively low-powered for use as a single unit on light duties but marshaled together to provide the power needed on a heavy train. With steam traction a single very powerful and expensive locomotive was required for the heaviest trains or the operator resorted to double heading with multiple locomotives and crews, a method which was also expensive and brought with it its own operating difficulties.
0-6-0+0-6-0
The only steam locomotive example of this type of engine in the United Kingdom was the Leader. It was originally commissioned by the Southern Railway but it was completed by British Railways in 1949. The locomotive was a class of experimental articulated steam locomotive, produced in the United Kingdom to the design of the innovative engineer Oliver Bulleid. The Leader was effectively a Meyer locomotive since both sets of drivers were articulated. It was built in an attempt to extend the life of steam traction by eliminating many of the operational drawbacks associated with existing steam locomotives.
The 0-6-0+0-6-0 configuration was also applied to diesel-electric locomotives when British Rail created the Class 13 in 1965. This was done by permanently coupling two Class 08 0-6-0DE shunting engines as "master and slave" units, the latter with its cab removed. In North American terminology, this is referred to as a "cow and calf" arrangement. The modification came about because of a need to provide more powerful shunting locomotives for the Tinsley Marshalling Yard.