The introduction of fibre optic systems is moving quickly on high capacity national and international trunk routes. This paper presents the evidence that the external plant needed for rugged civil and military requirements is now ready for implementation. The paper deals with the practical aspects of using the new transmission medium in rugged environments. The specialised long haul, high bit rate monomode PTT type system is specifically excluded. A brief survey of the possibilities offered leads to a definition of the relatively short haul defence and domestic systems that are needed now and for the foreseeable future. Special emphasis is paid to the performance of the external cable plant.