© Mapbox · © OpenStreetMap contributors · Boundary data © Cadw
Cilybebyll Auxiliary Unit Operational Base is a Second World War defensive installation located in Wales, protected by Cadw as a scheduled monument under reference GM620. The site forms part of the network of covert bases established across Britain to enable resistance operations in the event of enemy invasion. Built upon the South Wales Upper Coal Measures Formation, the underlying bedrock comprises mudstone, siltstone and sandstone interspersed with coal and ironstone layers, geology that shaped both the landscape and the region's industrial heritage.
The auxiliary units were specially trained volunteer forces tasked with sabotage and guerrilla warfare, operating from concealed bases near key strategic locations. This particular installation sits within the coal-mining heartland of South Wales, its position reflecting the economic and military significance of the region's mineral resources during wartime. The ferricrete and ironstone deposits within the bedrock spoke to centuries of industrial extraction in the area.
Today the site survives as physical evidence of Britain's home defence preparations and the scale of organisation required to anticipate invasion. The base exemplifies how wartime military infrastructure was integrated into the existing landscape, utilising the terrain and geology of industrial South Wales as both tactical advantage and concealment.
Cilybebyll Auxiliary Unit Operational Base is a scheduled monument protected by Cadw under reference GM620. View the official record →
Cilybebyll Auxiliary Unit Operational Base is a Second World War defensive installation located in Wales, protected by Cadw as a scheduled monument under reference GM620.
Cilybebyll Auxiliary Unit Operational Base dates from the post medieval/modern period, and is classified as a auxiliary unit site. It is one of over 32,000 scheduled monuments protected across the UK.
Cilybebyll Auxiliary Unit Operational Base is a Scheduled Ancient Monument, legally protected by Cadw — the body responsible for designating and safeguarding heritage sites in Wales. The official designation reference is GM620.
Several scheduled monuments lie within 10 km, including Neath Roman Site (6.6 km), Court Herbert Cross & Grave Slab (6.7 km), Neath Abbey (7 km).
This page is just one thread. A full Aubrey report pulls together 13 strands of Cilybebyll Auxiliary Unit Operational Base's history, each drawn from the record and mapped to the exact spot:
Every location is different. Not every section appears for every place, only what the historical record actually holds turns up in a report.
Cilybebyll Auxiliary Unit Operational Base stands on South Wales Upper Coal Measures Formation, bedrock that formed in the Westphalian. The rock here is mudstone, siltstone, sandstone, coal, ironstone and ferricrete.