The Walcheren Campaign was an unsuccessful British expedition to the Netherlands in 1809 intended to open another front in the Austrian Empire's struggle with France during the War of the Fifth Coalition. Around 40,000 soldiers, 15,000 horses together with field artillery and two siege trains crossed the North Sea and landed at Walcheren on 30July. This was the largest British expedition of that year, larger than the army serving in the Peninsular War in Portugal. The Walcheren Campaign involved little fighting, but heavy losses from the sickness popularly dubbed "Walcheren Fever". Although more than 4,000 British troops died during the expedition, only 106 died in combat; the survivors withdrew on 9December.
In July 1809, the British decided to seal the mouth of the Scheldt to prevent the port of Antwerp being used as a base against them. 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. However, the Battle of Wagram had already occurred before the start of the campaign and the Austrians had effectively already lost the war.
John Pitt, 2nd Earl of Chatham commanded the army, whilst Sir Richard Strachan commanded the navy, the full expeditionary force of 37 ships, the greatest which had ever left England, leaving The Downs on 28 July. Commanders included Hugh Downman, Edward Codrington, Amelius Beauclerk, William Charles Fahie, George Cockburn and George Dundas.
As a first move, the British seized the swampy island of Walcheren at the mouth of river Scheldt, as well as South Beveland island, both in the present-day Netherlands. The British troops soon began to suffer from malaria; within a month of seizing the island, they had over 8,000 fever cases. 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. Once it had been decided to garrison Walcheren Island in September 1809, Pitt was replaced by Lieutenant-general Eyre Coote who in October was replaced by Lieutenant-general George Don.
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. There were a few French units among those present considered to be of inferior quality as they were manned by the physically infirm and dregs of the training depots. However, on 10 August 1809, as reinforcements began flowing into the invasion zone, Napoleon approved the appointment of Marshal Jean-Baptiste Bernadotte, the Prince of Ponte Corvo, who had recently been stripped of his command after disobeying orders at the Battle of Wagram as overall commander of the invasion zone. Dismissed from Napoleon's Grande Armée, Bernadotte returned to Paris and was sent to defend the Netherlands by the council of ministers. His arrival gave the French a much-needed unity of command and he brought with him a genius for organization and training. Bernadotte led the reinforced and reorganized French forces competently and although the British had captured Flushing on the day of his arrival to the war zone after a ferocious bombardment, and the surrounding towns on 15 August, he had already ordered the French fleet to Antwerp and heavily reinforced the city. The French numbers were such that the main objective for the British, Antwerp, was now out of reach. The expedition was called off in early September. Around 12,000 troops stayed on Walcheren, but by October only 5,500 remained fit for duty.
In all, the British government spent almost £8 million on the campaign. Along with the 4,000 men that had died during the campaign, almost 12,000 were still ill by February 1810 and many others remained permanently weakened. Those sent to the Peninsular War to join Wellington's army caused a permanent doubling of the sick lists there.
A fleet of around 40 vessels, including sixteen 74 gun warships of the third rate, participated under the overall command of Rear Admiral James Bissett. A number of smaller vessels including customs-house and excise cutters were also involved, as was a packet ship. The City of London, Loyal Greenwich, and Royal Harbour River Fencibles also contributed men to the expedition.
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. It fought a rear guard action for several days but the battalion was almost completely captured. The Legion's brass band followed by the Irish battalion led the surrendered French garrison out of the town. However, a small party of Irishmen escaped and went into hiding with the battalion's cherished imperial eagle, and after a few days they crossed the Scheldt River and escaped. Commandant Lawless was presented to Napoleon and he together with Captain O'Reilly received the Légion d'honneur in gratitude.