*Duchess of Loughborough, commonly known as Duchess, is a large ivory-coloured tender engine that works on the Mainland. Her job is to transport the Royal Family to all their royal appointments.

Duchess is described as "a lovely, warm, bubbly sort of effervescent engine who is very anxious to get things right." Although friendly, she can be forgetful, and she strives to be on time. Her tendencies to hurry can sometimes make her seem like she has lost her manners. Despite this, she is good-hearted and very respectful, always looking to be the best she can.

Duchess is based on the London Midland and Scottish Railway (LMS) Coronation Class. Designed by William Stanier and built at Crewe Works between 1937 and 1948, these 4-6-2 tender locomotives were built for express passenger services and - on a test - were the most powerful steam locomotives ever used in Great Britain. They were in service until 1962 to 1964 when they were withdrawn from service and scrapped en masse. Three examples have been preserved, including No. 6229 Duchess of Hamilton at the National Railway Museum.

Duchess has some modifications from her original basis:

Her smoke deflectors are based on those used by the LMS Royal Scot Class. She has an LNER corridor tender of the same design as Flying Scotsman's. She also has circular buffers as opposed to oval ones, as well as a single chimney as opposed to the double chimney used on the Coronation class.

Duchess is painted ivory with gold lining and boiler bands. Her wheels, running plate, and buffer shanks are painted dark red, while her front bufferbeam is black. She has two golden nameplates with red backing, one on each side of her boiler, as well as a removable crown symbol on her front end when carrying the Royal Family. Her company's initials, LMS, are painted on her tender in gold with a red drop shadow, while her number is painted in gold on the side of her cab.*