Heljan locomotives feature a heavy diecast chassis block and twin motors, one driving each bogie. Weighing in at over 3 kilos the combination of weight and powerful motors results in a smooth running locomotive with significant inertia for realistic starts and acceleration.
Attention to detail in the design of the bodyshell to incorporate accurate profile, grilles and louvres results in a very pleasing model of the 37, which proved to be one of British Rails' most successful and widely travelled diesels.