Engine 6115 was built in 1927 by the North British Locomotive Company, and named for the Scots Guards the following year.
In 1936, she took a starring role in the film Night Mail, a documentary charting a London, Midland and Scottish Railway (LMS) over night mail train from London to Scotland.
Directed by Harry Watt and Basil Wright and with music by Benjamin Britten, the documentary also featured a WH Auden poem of the same name, which opened:
This is the Night Mail crossing the border,
Bringing the cheque and the postal order,
Letters for the rich, letters for the poor,
The shop at the corner and the girl next door.
The steam engine was rebuilt in 1947, and painted black. In 1948 she was renumbered 46115 by British Railways, and withdrawn in 1965.
She was purchased by the West Coast Railway Company, and restored to main-line running standard in 2008, completing her first test run in June of that year. The locomotive was repainted in BR Brunswick Green, hauling its first rail tour in August 2008 from Hellifield to Carlisle, and back.
She ran as a special for the centenary of the Girl Guides in September 2009, and was temporarily rebranded The Girl Guide.
One of two preserved Royal Scots locomotives along with the crimson lake-liveried 6100 Royal Scot, Scots Guardsman carried the Olympic torch in 2012 in place of the Flying Scotsman.