A “Walcheren Expedition” is a well-devised scheme, which is ruined by the stupidity of the agent chosen to carry it out. Lord Castlereagh's instructions were “to advance instantly in full force against Antwerp,” but Lord Chatham wasted his time and strength in reducing Flushing. Ultimately, the red-tape “Incapable” got possession of the island of Walcheren, but 7,000 men died of malaria, and as many more were permanently disabled.
(Source: Brewer's Dictionary of Phrase and Fable, 1898)