Underground Royal Observer Core post for monitoring nuclear explosions and fallout. The post was built in 1961 and abandoned in 1991. The site is now locked but instrument tubes are visible above ground. Previous post structure is part brick, part shuttered concrete construction. Possibly dating to the period between 1943-1953. Hamstreet site is one of 27 original used for training the newly established Royal Observer Core in 1925. Thought by the No1 group Royal Observer Core Association to be a world war 2 post. Summary from record TR 03 SW 30: This post structure approximates to a Type A Orlit, but is also of part brick, part shuttered concrete construction. It possibly dates to the 1943-1953 period. The Hamstreet site is one of the original 27 posts used for training the newly established Royal Observer Core (ROC) in 1925. The site is thought by the No1 Group ROC Association to be a world war II post. Within the same compound is a ROC underground monitoring post dating to 1961 (TR 03 SW 17).