The caves acquired a new lease of life during the Second World War when they were utilised as air raid shelters. By February 1941, 86 of the caves were available as public shelters. Older caves were re-opened and modified and new purpose-built tunnels were cut into the sandstone. The labyrinth of formerly isolated ancient caverns, which now exist beneath the city, may be a consequence of these modifications.
The newer caves were cut deeper than their ancient counterparts and are identifiable by their linear appearance. The largest of these was cut beneath the Player's factory in Radford and was capable of sheltering nearly 9000 people.
The sandstone excavated in the process of cutting caves was also a useful source of sand for sandbags, and a number of additional holes were dug to supply the demand.
The caves cut beneath the castle rock were fashioned like an extended gothic arch, in keeping with the appearance of the Castle Gatehouse. However, in 1953 their secret use was revealed:
"The Guardian was informed that a radium and radon extraction plant which had been stored in the caves since the war had been removed to the radio chemical centre at Amersham. Employees of the department had to wear masks, owing to the foul air in the caves".
Nottingham Guardian 14 July 1953
The discovery was met with great concern. Today the castle rock caves are home to a shooting range.
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