Ancient Monuments

History on the Ground

This site is entirely user-supported. See how you can help.

Cilybebyll Auxiliary Unit Operational Base

A Scheduled Monument in Cilybebyll, Neath Port Talbot (Castell-nedd Port Talbot)

We don't have any photos of this monument yet. Why don't you be the first to send us one?

Upload Photo »

Approximate Location Map
Large Map »

If Google Street View is available, the image is from the best available vantage point looking, if possible, towards the location of the monument. Where it is not available, the satellite view is shown instead.


Latitude: 51.723 / 51°43'22"N

Longitude: -3.8101 / 3°48'36"W

OS Eastings: 275067

OS Northings: 204247

OS Grid: SN750042

Mapcode National: GBR H2.2QCC

Mapcode Global: VH4JS.XY3J

Entry Name: Cilybebyll Auxiliary Unit Operational Base

Scheduled Date: 3 March 2011

Source: Cadw

Source ID: 944

Cadw Legacy ID: GM620

Schedule Class: Defence

Category: Observation Post

Period: Post Medieval/Modern

County: Neath Port Talbot (Castell-nedd Port Talbot)

Community: Cilybebyll

Traditional County: Glamorgan


The monument comprises the remains of an Auxiliary Unit Operational Base, which dates from the Second World War (1939-45 AD). It is situated 250m east-north-east of Plas Cilybebyll house where its location set below ground in woodland ensured that it was hard to detect. Operational bases were built in the coastal districts along the length of the British coastline where a German invasion was expected. The structure consists of a concrete floor, brick built end walls and entrance shaft, together with a curved corrugated sheet steel roof and side walls resting on low sills. It is aligned north-east by south-west and the entrance is located at the north-east end. Internally the structure consists of a single room that measures 4.25m in length, 3.07m in width and 1.95m in height. The collapsed remains of an escape tunnel lead away from the entrance in the south-west wall.

The monument is of national importance for its potential to enhance our knowledge of the British Auxiliary Unit organisation and the buildings it built and used. Very little is known about this organisation, due to the continuing secrecy surrounding its establishment and the fact that many operational bases were destroyed after the War. While a partial list of operational bases survives for Wales, this is one of very few where the location is known and the structure is in good enough condition to provide details of construction, form and layout. The remains are well preserved and retain significant archaeological potential, with a strong probability of the presence of associated archaeological features.

The area scheduled comprises the remains described and an area around within which related evidence may be expected to survive.

Source: Cadw

Other nearby scheduled monuments is an independent online resource and is not associated with any government department. All government data published here is used under licence. Please do not contact for any queries related to any individual ancient or schedued monument, planning permission related to scheduled monuments or the scheduling process itself. is a Good Stuff website.