MoD traffic and Devonport Royal Dockyard (Plymouth). The rail connection from the main-line at Keyham West GF is still in use. This connects to a branch into the Dockyard and to the nuclear submarine refitting docks. Traffic is related to the refuelling and defuelling of the reactors, where active waste is safely removed by rail to storage at Sellafield. There are no weapons involved. Movements are infrequent and always by DRS. Less infrequent are route knowledge/training runs.
Defence Muntions Ernesettle (Plymouth). A storage facility next to the river Tamar has a rail connection off the Gunnislake branch. The site is in use though the rail link could be described as mothballed, though can be bought into use if required.
Details of both sites above in the books: ’Devonport Dockyard Railway’; and ’Plymouth’s Hidden Railways’; both pub Twelveheads Press.
Also, for those not familiar with place name slang, Pompey = Portsmouth.