The Cilybebyll OB -  Neath and Port Talbot by Martin Locock

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The creation of a ‘coastal crust’ of defended and obstructed possible landing sites was supplemented by a series of ‘stop lines’, exploiting natural barriers enhanced by obstacles and strongpoints, to delay an invasion force and protect the central areas. The most significant of these lines was the GHQ line, running from Edinburgh and Bridgwater to London. In Wales, successive rivers were chosen, including the Rivers Wye, Usk, and Neath. The limited number of crossings were protected by pillboxes, and arrangements were made for the demolition of unwanted bridges.

The OB at Cilybebyll, in woodland 100m northwest of Plas Cilybebyll house (SN 750 043: it is on private land), survives in good condition (fig. 1); the author was invited to investigate the site by the landowner.  On the surface, the OB is visible as a slightly-raised area; at the north end, the shafts are visible as brick features, no longer hidden by a trap door.  There is little doubt that when constructed it would have been concealed from all but the closest scrutiny (fig. 2).

The interior now has a flooded floor.  A winch arrangement on the entrance wall survives; this may have been attached to an aerial for radio communications or to the trap door.  An alcove on the east side of the door may have been for the radio equipment. 

Figure 1. Interior showing corrugated iron roofing and escape opening.

Figure 2: The surface, showing escape shaft

THE ROLE OF THE CILYBEBYLL SITE

Although no documentary evidence for the OB has been located, its location is significant, in wooded land to the north of the Neath valley.  Had an invasion force arrived in southwest Wales (perhaps using Milford Haven as a deep-water harbour, and perhaps starting from Eire, as was feared at the time), it would have encountered resistance at Carmarthen - New Quay , Ammanford, the River Loughor, the Swansea valley, the Neath valley and the River Taff.

Each stop line would have forced a delay while a set-piece assault was prepared.  If the small number of bridges strong enough to take tanks were demolished, temporary engineering works would also have been required; one of the key functions of the pillboxes guarding river crossings was to prevent their seizure by parachute forces to forestall their demolition.

Thus it was planned that the invading force would have been held up on the west bank of the Neath valley for days or weeks; in the meantime, the Auxiliary Unit patrol would have numerous opportunities to cause further disruption and delay.

The occasion for use did not occur; there was some discussion in the latter stages of the war about the future of the OBs, along with the disbanding of the Auxiliary Units, and although demolition of the sites was proposed, many seem to have been simply abandoned, and survive as monuments to a short period when the tranquil landscape of the Neath uplands was viewed as a possible battle zone.

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