Although imaginary, St Marnock Engine Shed had good reason to exist. The Ayrshire town of Kilmarnock, in steam days, was an important junction on the ex G&SWR  Anglo -Scottsh route from Glasgow to Carlisle.

It was served by Hurlford engine shed, but this was situated some miles to the South. With all the express passenger and freight traffic passing through Kilmarnock, it would have been of great benefit to have locomotive servicing facilities close to the station. St Marnock provides that.

The shed itself is a three road structure, featuring the cathedral style Galloway architecture, typical of the ex G&SWR sheds at Ayr, Hurlford and Dumfries, and, like those depots, it fuels its locomotives from a basic wooden coaling stage. Unusually for a small depot, it boasts a 70 foot turntable, capable of handling the largest express locomotives.
St Marnock does not have its own locomotive allocation, but plays host to visitors from Ayr, Hurlford, and the principal Glasgow depots. Making regular appearances are visitors from major depots south of the border, like Carlisle Kingmoor and Upperby, Leeds Holbeck and Crewe.
The locomotives that can be seen at St Marnock reflect the wide variety of motive power passing through Kilmarnock in the sixties: Ayrshire based “Crabs” and “Black Fives”, Standard and ex LMS tank locos, and express engines including “Duchesses”,  “Royal Scots”, “Jubilees”, “Britannias”, “Clans” and ex LNER Pacifics including the “A3s” which were briefly allocated to Leeds Holbeck for  working the Thames-Clyde Express.

The layout is built on three 5foot x 3 foot baseboards, with plywood tops on timber frames, giving a scenic area of 15  ft.x 3 ft. At each end, there is a 2 foot extension board for the storage of locomotives moving to and from the shed area.
Peco track and pointwork is used throughout, with the points being operated by Fulgarex slow motion motors.
The main shed building is built from sandwiched layers of cardboard with an outer finish of  course stone embossed plastic  sheet.   The coaling stage is also of card, with the planking  produced from strips of balsa wood. Card is also used extensively in the other buildings.
The turntable is an accurate model of a Ransome and Napier turntable, built in brass by Metalsmith.
The layout is lit along the scenic area by concealed striplights.