Llananno Royal Observer Corps Monitoring Post

Cadw's description

Summary description and reason for designation

The following provides a general description of the Scheduled Monument.

The monument comprises a Royal Observer Corps Orlit A surface observation post and adjacent underground monitoring post. Both date to the Cold War era and are located on a local summit adjacent to an existing field boundary. The Orlit A post (Item A) was used between 1952-60 and is located within its own fenced compound, which measures 5.6m in length (N-S) and 5.3m in width. The access gate is on the N side. The Orlit post was a rectangular building that measured 1.6m in height, 3.05m in length (E-W) and 2.03m in width (N-S). It was constructed of bolt-together prefabricated concrete panels. The S-facing entrance led into a smaller roofed section on the W side, used as a shelter and store. A second doorway provided access into an open observation section on the E side. The underground monitoring post (Item B) was built in 1960 and decommissioned in 1991. It is located immediately to the N of Item A within another compound, which measures 19.9m in length (N-S) and 18.4m in width. The access gate is on the N side. The upper surface of the post is protected by a grassed mound of earth and rock, which measures 1m in height, 15m in length (N-S) and 14m in width transversely. The combined entrance, ventilator stack and Ground Zero Indicator mount are located at the S end. A second ventilator stack is located at the N end. The mounts for the Fixed Survey Meter probe and Bomb Power Indicator are located between. The connector box on the W side of the N ventilator stack, together with three concrete anchor posts for the VHF aerial mast demonstrate that this was a Master post.

The monument is of national importance for its potential to enhance our knowledge of the development, reappraisal and renewal of British Cold War defence systems. The successful development of a national network of underground monitoring posts represents one of the chief British technological achievements during the Cold War period. It marked the important transition between the Royal Observer Corps' traditional aircraft monitoring role and the organisation's reorientation toward monitoring the detonations of nuclear bombs and the drift of radioactive fallout. The remains of the individual structures are well preserved and retain significant archaeological potential, with a strong probability of the presence of associated archaeological features and deposits. The Orlit A post is a rare survival and it possesses important group value with the underground monitoring post.

The area scheduled comprises the remains described and an area around within which related evidence may be expected to survive. The scheduled area is roughly rectangular in shape and measures 31m N-S by 22m transversely.