Llanberis RAF Reserve Depot
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In 1939 The Air Ministry sought approval to acquire the disused Glynrhonwy Isaf Slate Quarry which had closed in 1930. For use as a bomb storage facility.
At the time Llanberis was deemed suitable for the storage of 18,000 tons of bombs. It consisted of a number of deep open pits, linked together by tunnels. Following the apparent success of the design employed at Harpur Hill in Derbyshire, the air ministry decided to use the same technique at Llanberis. Converting the eastern pit into an underground depot, but because of the great depth of the quarry the design was adapted to produce a structure with two floors throughout.
On 25th January 1942, two-thirds of the structure collapsed within seconds under the weight of the overlaying backfill. Completely engulfing a train of twenty seven wagons which was in the process of unloading. The collapse buried over 14,000 tons of bombs which at the time represented 14% of the total RAF stock.
Most of the bombs were recovered and although the remaining tunnels were eventually cleared of debris. No munitions were stored underground at Llanberis again. The surviving underground galleries were abandoned and the collapsed section was used for open storage of incendiaries and as a demolition area.
After the war a small RAF detachment of bomb disposal experts remained at the depot clearing dumped weapons. After the war large quantities of incendiaries were dumped into the pits.
By 1955 all functional stock was removed from Llanberis and the depot closed a year later. But in 1969 a decision was taken to clear the entire site of explosives and explosive debris.
The task was given to 71 Maintenance Unit EOD Flight from Royal Air Force Bicester. Royal Navy divers were also co-opted to investigate the contents of a large lake in one of the pits as it was suspected that it might contain some explosives.
The divers reported that the bed of the lake was littered with explosive including a number of large bombs. Subsequently, over 20,000,000 gallons of water and sludge were pumped out.
By April 1973 the lake was emptied revealing everyone's worst fears; it took a further two years to recover and dispose of the explosives revealed. Fortunately this pit was one of those that 38 Engineer Regiment (RE) had constructed. Otherwise the task would have been impossible.
The RAF finally left Llanberis in 1975 after spending over 20 years clearing the site from buried munitions.
