One of the finest surviving anti-invasion lines in the UK, with the anti-tank blocks nearly all in their original positions and two of the five original pillboxes still substantially extant.

The line of anti-tank blocks extends for 2.4km along the crest of the shingle bank (NPRN 270840). The aerial photographic collections of the National Monuments Record of Wales suggest that the line was begun after July 1940 (RAF Medmenham M286 H5 1 July 1940). The nationwide construction programme of such defences caused a crisis in stocks of cement, with many contractors working 7-day per week, 12-hour days, to complete the plans drawn up by the Home Defence Executive under the command of General Sir Edmund Ironside, Commander-in-Chief Home Forces. It was common for all local able bodied men, boys and women to be drawn into the work. The flat tops of several of the blocks feature the inscribed initials of some of the builders - 'Thomas Roberts', 'Betty Price', 'D Pant', 'DW 1940' and 'LW 1940'. The blocks would have been constructed in four stages using a mold and large beach stones with an infil of pebbles. Where the outer layer of concrete has deteriorated, the banding of the phases can be seen.

When constructed, the line comprised 691 blocks, each a standard size, trapizoid in section 1.7m high and 1.5m x 1.5m at the base, tapering to 0.9m x 0.9m at the top. The spacing bewteen blocks is approximately 1.35m. One of the blocks has been moved to provide easier acess to the beach - it has been calculated that each block weighs approximately 1.5 tons. The line runs from SH61101201 in the south out along the spit to terminate at SH61081433. At the southern end of the line, many of the blocks are exposed to their full height and eight have been toppled to improve beach defences. As the line moves northwards, some have become engulfed by the shingle bank, or covered by wind blown sand and begun to be grassed over.

There are five standard FW3/24 pattern pillboxes set into the defensive line - one is in good condition, one substantially altered, with feint traces of other three still discernable at their former locations. The southernmost pillbox (NPRN 270355) at SH61101203 is a standard hexagonal Type FW3/24 - that is brick-built, with a double skin made of concrete and rubble infill. Two of the front walls have been removed and the remaining firing loop and entrance have been filled in. There is no trace of the internal anti-ricochet wall, except for marks on the floor and ceiling. From this pillbox, there are 148 concrete cubes until the next (NPRN 270356). This structure is in good conditon, but the two firing loops on the rear wall have been blocked. From this pillbox, there are 161 blocks until the next pillbox at SH61101307 (NPRN 270353). This pillbox defended access to the road running along behind the shingle ridge as it curves inland. Only the concrete raft foundation remains. Continuing north, there are 156 block to the feint traces of the next pillbox at SH61041361 (NPRN 421535). Only part of the foundation and a few fragments of red bricks remain. The last pillbox was situated 151 blocks northward again (NPRN 421536). Aerial photographs dating to 1950 show the pillbox leaning over, probably due to subsidence of the shingle ridge and coastal erosion Although demolished (perhaps by explosives), a few large fragments of the structure can still be found. After this point, there are a further 53 blocks until the line terminates.

Sources include:
Defence of Britain Project (Record Number 3242)
Parry, M, 2013, World War II Defences of the Shores of the Mawddach Estuary, RCAHMW Collections
Redfern, N I, 1998, 20th Century Fortifications in the United Kingdom Vol II, Site Gazetteers Wales, Council for British Archaeology
Ruddy, A J, 203. British Anti-Invasion Defences 1940-1945, pg4-6
Wills, H and Cooper, L, 1985, Pillboxes - A Study of UK Defences

RCAHMW Aerial Photographic Collections:
RAF 106G/UK/1468, Neg Nos: 2202. 6201-2
RAF 540/373, Neg Nos 120-127
RAf 540/394
Ordnance Survey 76-120, Neg Nos 024-027

Maritime Officer, RCAHMW, March 2016.