The Walcheren Campaign (Dutch pronunciation: [ˈʋɑlxərə(n)]) was an unsuccessful British expedition to the Kingdom of Holland in 1809 intended to open another front in the Austrian Empire's struggle with France during the War of the Fifth Coalition.

John Pitt, 2nd Earl of Chatham, the commander of the expedition, was ordered to capture the towns of Flushing and Antwerp and thus enable British ships to safely traverse the Scheldt River.

A British expeditionary force of 39,000 troops, together with field artillery and two siege trains, crossed the North Sea and landed at Walcheren on 30 July.

[2] The primary aim of the campaign was to destroy the French fleet thought to be in Flushing whilst providing a diversion for the hard-pressed Austrians.

The British troops soon began to suffer from "Walcheren fever", due to the symptoms present most likely a combination of malaria, typhus, typhoid and dysentery.

The medical provisions for the expedition proved inadequate despite reports that an occupying French force had lost 80% of its numbers a few years earlier, also due to disease.

[2] At the time of the initial landings, the French forces were characterized by a divided command over a motley crew of units manned by soldiers of many nationalities spanning French-occupied Europe.

[7] The debacle was also a source of acute political embarrassment, in particular for Lord Castlereagh upon whom the former United Irishman, Peter Finnerty, who at the invitation of Sir Home Popham[8] accompanied the expedition as a special correspondent for The Morning Chronicle, heaped the blame.

[17] The 1st battalion of the Irish Legion (raised by the French for an invasion of Ireland that never happened) was stationed in Flushing during the assault and received its baptism of fire there.