Site Records

SiteName: Llanberis RAF Reserve Depot (Bomb Store)

FFord Clegir
Llanberis, Caernarvonshire
OS Grid Ref: SH566610

Sub Brit site visit July 2000

SITE VISIT: The obvious part of the site resembles eight parallel railway tunnels opening out into a vast concrete lined tank about 100 metres by 60, with walls 12 metres high; this was the area of the collapse that was subsequently cleared. Inside, the remaining galleries are very dry, clean and in good condition, with limited graffiti and no vandalism and little litter; the walls in the tunnels are all painted white. The lower level is about 15 feet from floor to ceiling, with walls running the full length separating the galleries.

Each gallery is about 24 feet wide and over two hundred feet long, ending in a thick brick wall, which was built to separate the surviving galleries from the collapsed area. There is a wider area between gallery B and gallery C which brings a sunken standard gauge railway line into the storage area, the floor of the depot acting as a loading platform either side of the line. Except in this wider gallery, concrete pillars about 12 feet apart run down the centre, supporting a concrete beam running the length of each gallery. These help to support the ceiling, which forms the floor of the level above. They are apparently original, because each corner has a steel rubbing piece built in, as do the other openings but not the brick reinforcements seen in some places, which I believe to have been installed as strengthening after the collapse. The sidewalls have square openings about 15 feet wide every so often, some of them bricked up. The galleries are lettered A to H on the lower level and J to S on the upper level.

Each gallery was numbered into eleven bays. The bay numbers can be clearly seen on the walls, but there is no divider between the bays except a red roundel painted high on the wall midway between the numbers. The numbers run from 6 to 11 on upper and lower levels, leaving bays 1 to 5 in the open area where the collapse occurred. Roughly two thirds of the original underground area is now open to the air (the 'tank').

There are two galleries to the right of the railway line, A and B downstairs and J and K upstairs. The furthest right is J gallery upstairs. A / J is much shorter than the other galleries. It has only bays labeled J8, 9 and 10. At the back, part of the floor is raised with steps up to it and this is a blind gallery, running forward only as far as J8. The others all run from 11 to 6 before ending in the brick wall, but for gallery J there is no brick wall and no external sign at all. J10 is also not full width. My guess is that the original quarry was slightly wider here, and the builders took advantage of the extra space.

Gallery M has two lifts. One is at C6 / M6, hard up against the brick wall and barely any use. Surprisingly, no effort appears to have been made to open the other side of the lift so that it could have been used more readily. As the brick wall was built after the collapse this may confirm that the remaining underground section of the depot was abandoned. The other lift is at C9 / M9. A third lift was in the collapsed section and has been lost. The wiring is very old, gutta percha insulation and no sign of post-war modernisation.

The upper level galleries are the same width as the lower, but they have an arched roof and there is no line of central pillars as in the lower galleries. The doorways between the galleries are smaller than below, and arched rather than square. Several have been reinforced after the original build with four courses of brick, also formed into an arch, but without the steel corners seen on the original concrete construction. This brickwork narrows the opening from 12 foot to six foot wide, and drops the height of the arch from 11 to 7 foot. Around M, N and P several of the archways are completely bricked up. There is a single staircase between lower and upper levels, at C11.

There are some few electrical fittings left. Mains power came in through the back tunnel where there is a vertical cable shaft. Most of galleries show signs of tubular conduit for hanging lights, and a few of the reflectors remain. All of the switches have gone, except the casing of one which shows clearly that it was of the type used in furls and explosives stores, which contains the spark inside the housing.

Two bits of official graffiti have been painted on neatly, and again are likely to date from 1942. They say that the practice of spitting is disgusting and must cease. Anyone caught spitting will be dismissed. This points to a mainly civilian workforce, since dismissal is not the term that would be used for a serviceman facing a charge.

There are three tunnels leading to the main storage space. Two open into the 'tank'; the open part where the collapsed concrete, bombs and slate backfill have been removed. The main access tunnel is about 15 feet wide, square section part of the way and is arched the rest. The northern tunnel was adapted to take a standard gauge railway line during the construction of the depot. It is quite short with a bend and has been shotcreted, probably after the closure of the depot.

The southern access tunnel is smaller and originally took a narrow gauge quarry tramway into the eastern pit; although it can still be entered from the depot, the other end has been backfilled with waste stone. After the bend the tunnel is concrete lined and arched, with signs of decay in the concrete. Reinforcing rods could be seen, about 3cm thick and 12 cm apart. When the slate quarry was still in use these tunnels served the Glynrhonwy Isaf mill on the west side of the A4086. The mill was extended and altered for munitions manufacture and has now been rebuilt for industrial use. The tramway originally continued to Llanberis Lake which was used for tipping slate waste.

The third tunnel is at the back of the storage area in gallery D, and is mostly unlined rock. It is about 7 feet high. The floor is very rough concrete, but there are rotten wooden sleepers set into the concrete. An open water channel runs on one side, with water running into the workings to the start of the tunnel, where it drops into an inspection pit and is carried away in a large earthenware pipe about a foot in diameter. It is the noise of this falling water that you hear throughout the upper galleries, sounding at first as if fans were running. At the bend of the tunnel, the straight passage is bricked off, while the open tunnel bends to the left and goes into the open air past a vertical shaft up which power cables ran. As well as forming the emergency exit from the depot this tunnel was also used for the painstaking removal of the munitions after the collapse. Significantly, the floor of this tunnel is not level with the floor of the storage galleries, being about a foot higher. This would have added to the handling problems getting the munitions out in the recovery operation.

The back pit is about seventy feet deep and maybe 100 feet square. Off to the right is another adit, leading slightly downwards and filled with water, with no sign of an exit. Each of the eight or more pits in the old quarry was linked by a similar tunnel.

Back outside in the 'tank', there is little to see. The space between the railway platforms has been filled with rubble and floor was clear but has had a quantity of spoil tipped there. On the walls are the remains of wooden signboards every few feet, which would have been bay labels (unlike the ones inside, which are painted). This confirms that the cleared open area was used from 1943 for storage of incendiaries.

In August 2003 the two access points into the surviving underground section of the depot were grilled and gated in an attempt to prevent access into the tunnels.

For further pictures of this site click here

Sources:
Secret Underground Cities by NJ McCamley ISBN 0 85052 585 3
The Slate Regions of North and Mid Wales by Alan John Richards ISBN 0 86381 552 9
Designed to Kill by Major Arthur Hogben ISBN 0 85059 865 6
Subterranean Wales web site

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