The Hanover Expedition, also known as the Weser Expedition, was a British invasion of the Electorate of Hanover during the Napoleonic Wars. Coordinated as part of an attack on France by the nations of the Third Coalition against Napoleon by William Pitt the Younger and Lord Castlereagh, planning began for an invasion of French territories in July 1805. Hanover, previously a British possession, was chosen as the goal of the expedition, with Swedish and Russian forces under Gustav IV Adolf and Alexander Ivanovich Ostermann-Tolstoy brought in to support the endeavour. Key to the success of the invasion was the support of Prussia, a nation poised to threaten France but not as yet openly hostile to the country. Sir George Don commanded the British expedition and he arrived with an army of around 14,000 men at Cuxhaven in November. To bolster the expedition and to strengthen the resolve of Prussia, Don's army was reinforced by 12,000, with Lord Cathcart taking over command.
Coordination between the British, Swedes, and Russians in Hanover was so poor that by December very little past the occupation of Hanover had been achieved. Cathcart grouped his force around the Weser, and soon after learned of the Austro-Russian defeat at the Battle of Austerlitz, which forced the Austrians to surrender and the Russians to retreat into Poland. With no large armies now protecting Cathcart's force from French attack, the situation was exacerbated when Prussia signed the Treaty of Schönbrunn with France, which created an alliance between the two nations and agreed that Prussia should control Hanover. With French and Prussian forces moving against Hanover, Cathcart's army was recalled in January 1806. The evacuation was completed on 15 February, and Hanover was left to the occupation of a Prussian army. The expedition, while a total failure, had little effect on the British position because of the lack of combat. Its method of quick amphibious transportation and landings of troops on a foreign shore would go on to be imitated in the Walcheren Expedition in 1809.
Background
In the first years of the French Revolutionary and Napoleonic Wars Britain found increased difficulty in engaging France in land battles. With British control of the seas and with many of the French colonies already taken because of this, France provided little opportunity for Britain to attack her apart from at sea. The small British Army was not equipped to engage in an invasion of the highly defended French mainland, and so continued to rely on the Royal Navy's blockade of Brest as the best way to impact the French at home. This outlook changed in 1803 when Austria and Russia allied themselves to Britain as part of the Third Coalition. With more militarily impressive allies now available to take the war to France on land, the British Army would be able to do the same, safe in the knowledge that it would not be engaging the French armies alone. This combined with the creation of the King's German Legion in 1804 produced an opportunity for new British Army operations. In around October 1805 Napoleon's planned invasion of the United Kingdom was called off and the French army left its encampments at Boulogne to march towards the Russians and Austrians.
With the largest portions of the French army gone, an opening was created for a British incursion into North-West Germany, with particular interest in the re-taking of the Electorate of Hanover, which George III had controlled until 1803, and which had only 4,000 French troops remaining in it. The British Prime Minister, William Pitt the Younger, and his Secretary of State for War and the Colonies Lord Castlereagh, were strong supporters of the enterprise, having championed it from as early as July. They envisaged an amphibious army that could be landed at points across Napoleonic Europe, making "pinprick" attacks against enemy targets while avoiding large battles with the French that could result in "crippling defeat". With news of the French withdrawal having reached Britain before its culmination, Castlereagh began planning in September. By taking Hanover, Britain could restore the country to its rightful rulers while also gaining a useful springboard for further operations in Europe. Not all of the establishment was in favour of the endeavour, with the Commander-in-Chief of the Forces, the Duke of York, relying on his experience in the Flanders campaign, arguing that expeditions that relied too much on the allies' actions would be difficult.