In order to haul heavier trains and compete for the coal traffic into London, the GER asked William Adams to design a locomotive capable of hauling a train of 400 long tons net (700 tons gross).

Tests were carried out with 265 class 4-4-0s to ensure that such trailing loads were feasible, followed by a prototype 2-6-0 number 527.

[2] As the design was novel, unexpected problems were encountered; the steam pipes to the cylinders constantly worked loose and were inaccessible for repair, condensation occurred in the cylinders, and these combined with a relatively small grate area and boiler barrel diameter with a long barrel led to poor steaming and high coal consumption.

This lone engine, used on heavy trains between Jemelle and Arlon on the Luxembourg line, performed poorly.

It featured a steam reservoir perched atop the boiler and a firebox made of refractory brick and surrounded by air instead of water.