It is the last industrial narrow gauge locomotive to be built for commercial use in the UK and is constructed to a modified Meyer articulated design.

The Meyer design for articulated locomotives uses two swivelling power bogies, with the boiler, water and coal supplies on a rigid frame above this, similar to how most large diesel or electric locomotives are now constructed.

None of the firebox or ashpan needs to protrude below footplate level, avoiding interference with the rear bogie.

[1] Monarch was delivered on 31 July 1953 and worked for a mere 13 years until being purchased by the Welshpool and Llanfair Light Railway in 1966.

The engine was dismantled for this purpose but then priorities changed, and despite later thoughts of using it on the Welsh Highland Railway the loco was left in parts whilst it slowly rusted.