A member of the GWR Castle class, 5080 was originally named Ogmore Castle. It was built at Swindon in 1939 and was allocated to Old Oak Common depot in London. It was responsible for hauling express passenger and goods trains over the GWR network. In 1941, it was transferred to Cardiff and renamed Defiant to commemorate a type of plane which fought in the Battle of Britain. It remained in South Wales for the rest of its service life.
It was withdrawn in 1963 and initially sold for spare parts. However, eventually it was restored and ran in steam for a number of years until its certificate ran out. It is now on static display at the Buckinghamshire Railway Centre.
