The British Rail Class 115 diesel multiple units were 41 high-density sets which operated the outer-suburban services from Marylebone usually to destinations such as High Wycombe, Aylesbury and Banbury which are on the Chiltern Main Line and Great Central Main Line. Sometimes, these sets used to operate 8- or 12-car-long expresses to Nottingham Victoria in the final years of the GCML. Coincidentally, Class 115 units operated services under Table 115 in the British Rail timetable.

Marylebone station is a Central London railway terminus and connected London Underground station in the Marylebone area of the City of Westminster. On the National Rail network, it is also known as London Marylebone and is the southern terminus of the Chiltern Main Line to Birmingham. An accompanying Underground station is on the Bakerloo line, sited between Edgware Road and Baker Street stations in Transport for London's fare zone 1.