| Operation Chastity | |||||||||
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| Part of Operation Overlord on the Western Front during the Second World War | |||||||||
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 United States |
 Germany | ||||||||
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Operation Chastity was a World War II plan by the Allies to seize Quiberon Bay, France, enabling the construction of an artificial harbor to support Allied operations in Northern France in 1944.
The artificial harbor was not developed, as the US VIII Corps failed to capture German-held areas that threatened the port. By the end of August 1944, Allied forces had captured all of Brittany except for the critical areas, preventing the further development of the operation. Following the capture of Antwerp and its port facilities in early September 1944, Operation Chastity was officially cancelled on 7 September.
The non-completion and eventual cancellation of Operation Chastity exacerbated strains on the Allied logistical system, may have prevented an Allied victory over Germany in 1944, and has been described as "the critical error of World War II", although other historians believe that priority was rightly given to the pursuit of the routing German forces.