Saint-Leu-d'Esserent is a commune in the Oise department in northern France.
Saint Leu is notable for 3,000 square metres (32,000 sq ft) of mushroom caves under the Thiverny plateau.
During World War II, the caves were one of three major underground V-1 flying bomb storage depots. In addition to the caves, the facility included blockhouses, bunkers, flak emplacements and railway links. Allied intelligence firmly identified late in June 1944 that Saint-Leu-d'Esserent and Nucourt were V-1 storage depots. On 27 June 1944, Saint-Leu-d'Esserent was initially bombed by the US Army Air Force, then on July 4/5 1944 by two RAF forces (the first unsuccessfully used Tallboy bombs in an attempt to collapse the limestone roof of the caves). Finally on 7 July 1944, an evening RAF raid successfully blocked the tunnels.
The storage dump at Thiverny was bombed in 1944 on May 5, July 11, July 12, and July 19.
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