A former Royal Observer Corps underground observation post is located to the north of Sleaford, in Leasingham parish. The post is believed to have been opened in 1961. Access was through a 2ft square hatch on the surface, where an associated air vent would have been visible. A ladder would lead down the concrete shaft to two rooms; the first being quite small and used to house the chemical toilet. The second, much larger monitoring room measured approximately 15' by 7'6'', and would have been staffed by three observers. The post remained in use until 1968, when it was closed and locked. {1}{2}