Short answers, pulled from the story.
The Walcheren Campaign was a British military expedition to the Kingdom of Holland in 1809. Its primary objectives were to destroy the French fleet at Flushing and to seize Antwerp, denying Napoleon a major port on the Scheldt. Britain also aimed to relieve pressure on its Austrian allies, who were fighting France in the War of the Fifth Coalition.
The campaign failed because of indecisive British command under John Pitt, 2nd Earl of Chatham, who spent two weeks besieging Flushing rather than advancing on Antwerp. Marshal Bernadotte, appointed French commander on the 10th of August 1809, concentrated nearly 100,000 men in Antwerp, making any British advance impossible. Walcheren fever also killed more than 4,000 British soldiers while combat claimed only 106.
Walcheren fever was most likely a combination of malaria, typhus, typhoid, and dysentery contracted in the swampy terrain of the Scheldt delta. Within a month of landing, the British army recorded more than 8,000 fever cases. More than 4,000 British soldiers died during the campaign, and only 106 of those deaths were caused by combat.
John Pitt, 2nd Earl of Chatham, commanded the British army, and Sir Richard Strachan commanded the navy. Britain deployed 39,000 troops and a fleet of 37 warships, the largest British expeditionary force of that year.
The British government spent almost £8 million on the Walcheren Campaign. More than 4,000 British soldiers died, almost all from disease rather than combat. Almost 12,000 survivors were still ill by February 1810, and many others were permanently weakened.
Marshal Jean-Baptiste Bernadotte, Prince of Ponte Corvo, was appointed French commander of the invasion zone on the 10th of August 1809. He concentrated up to 40,000 men in Antwerp, ordered the French fleet there, and organized the city's defenses against any British advance. Napoleon dismissed him on the 11th of September 1809 for an Order of the Day Napoleon considered an act of dangerous vanity.