Sites illustrated in the book include the vast Corsham network in North Wiltshire: the army ammunition depots at Monkton Farleigh, Eastlays, Ridge and Tunnel Quarry (which had its own underground railway station linked to the Bristol to London main line); the Spring Quarry underground aircraft engine factory - reputedly the largest underground factory in the world; Copenacre and a whole series of other Admiralty stores in North Wiltshire, and the museum repository at Westwood which housed all the treasures from the British Museum, the V&A and some forty other London museums and Galleries. Also included are the series of ill-fated RAF underground bomb stores at Llanberis, Harpur Hill, Chilmark and Fauld in Staffordshire which exploded in 1944 with catastrophic consequences. Amongst the other sites described and illustrated are the National Gallery's secret repository at Manod quarry, high in the Snowdon mountains; underground factories at Drakelow near Kidderminster, Longbridge in Birmingham, and Westwood near Bradford-on-Avon; subterannean naval weapons stores in South Wiltshire and West Wales and the highly secret underground chemical weapons storage tunnels at Rhydymwn near Mold.
Illustrated with approximately 400 colour and B&W archive photo's along with original engineers drawings and plans. Many of the archive photographs originate from the collection of the late F.W. Allan, who was chief engineer in charge of construction of most of these sites on behalf of the Ministry of Works and who commissioned them between 1936 and the late 1960s as a permanent record of the work undertaken. Gaining access to many of these sites in recent years to obtain contemporary photographs has frequently proved both physically and administratively tortuous.