The three military firing ranges encompass much of north Dartmoor and they have done for a very long time. Many of the structures associated with the military's activities can be classed as 'archaeological features' which include target railways, butts, bound stones and the observation posts or OP's as they are known on the moor. Originally these were granite built 'bunkers' where on the Okehampton firing range military personnel could observe any firing activities that were taking place as well as keeping a look-out for any stray animals or ramblers that might be wandering into the line of fire. Latterly the modern structures tend to be made of steel and have replaced the old design. Indeed many of the original OP's have been removed completely. At one time there were around 23 observation posts on Dartmoor, today there are just 7. The rest were removed either by the Ministry of Defence or the National Park Authority because some people considered them an eye-sore and spoilt the natural beauty of the landscape. This pic is Op 17. Devon, Uk