The original intention was for the Hymeks to replace steam locomotives in the Bristol area, west of Newton Abbott, and in South Wales, taking parcels and freight services within each area, and also passenger services to and from London. On introduction in 1961 the first locomotives were employed on secondary passenger services based around Bristol, such as Paddington to Hereford and semi-fast services to the west of England and Wales. Once they had proved themselves more than capable of handling these duties, they were also assigned to express Paddington-Cardiff-Swansea services, displacing King-class steam locomotives. These duties were heavier than they were designed for, and the Hymeks were displaced when Western and Brush type 4 locomotives became available to allow accelerated timings.