EM was developed because OO gauge, favoured by manufacturers of British prototype models, utilised track that was too narrow.

OO was developed in the UK in the 1930s as a response to manufacturers finding they were unable to fit the motors of the time into British prototype small boilered locomotives when scaled at the globally popular HO scale's 3.5 mm to a foot (1:87).

[2] This was mostly an issue for steam locomotives, where the popular technique at the time of making connecting and coupling rods from rail required an excessive spacing between wheel faces and the cylinders.

[2] More critically, small flanges required comparably smaller rail, trackwork gaps and point frogs in order to work reliably.

Modellers in EM typically re-wheel their rolling stock and hand-build their trackwork, although pre-built track is available from specialist suppliers.