The Blockhaus d’Éperlecques was a giant bunker built by Nazi Germany between March 1943 and July 1944 and was originally intended to be a launching facility for the V2 ballistic missile.
It was designed to accommodate over one hundred missiles at a time and to launch up to thirty-six a day all destined to land and explode on London and the South-East of England. The facility was designed to incorporate a liquid oxygen factory and a bomb-proof train station to allow missiles and supplies to be delivered from production facilities in Germany.
Have Bag, Will Travel 
I saw a documentary on these some time ago. What minds!
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Indeed!
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