Along with the rest of the Great Eastern Railway, the branch became part of the Southern Area of the London and North Eastern Railway when the various British railway companies were grouped into four large companies in 1923. The line was heavily used during World War I and World War II, with extra Air Ministry sidings provided at Dereham in 1943. In the early days of the war, Dereham was used as a reception centre for the construction materials used to build the local airfields.