The first permanent link between the United Kingdom and mainland Europe is currently under construction. It will consist of two railway tunnels and a central services tunnel, each some 50 kilometres long. The Folkestone and Calais terminals will be connect to the motorway and railway networks and the system will be used by three types of traffic: international passenger trains, international freight trains and road vehicles on special shuttle trains. The Channel Tunnel is expect to cost more that £5.2 billion and is schedule to open in mid-1993. Understandably, the economic implications of the system are being widely debated. In contrast, attention rarely focuses on the defence aspect.