When the Jubilee Line was opened, it was run with 1972 trains. In 1984 the 1972 trains were replaced by the new 1983 trains. The old 1972 Stock were used on the Northern Line. The 1983 trains proved to be unreliable in service, with their single doors making passenger loading and unloading slower than on other trains with wider doors. With the opening of the Jubilee Line Extension, the opportunity was taken to introduce new trains, and today the line is worked by 1996 trains.