Royal Common, just outside Elstead, is part of the Longmoor Training Area owned by the Defence Estates, which also covers large parts of Hankley, Elstead and Ockley commons. Public access is allowed across the Defence Training Estate provided you adhere to the Surrey Commons Military Lands Byelaws 1978. Army training here (when it takes place) revolves around logistics and minor infantry manoeuvre exercises and you're unlikely to come to any harm, but make sure you follow the instructions of troops if you do encounter any.