The battle of Copenhagen in 1801 and Nelson’s voyage to Reval were only a prelude to the main event, and not the decisive blow it seemed at the time, for after a short interval of peace they were succeeded by an even greater Baltic crisis. This produced an intensification and widening of British involvement in the Baltic in the next bout of warfare (the Napoleonic Wars). One of the results of the assassination of Tsar Paul and of the battle had been the collapse of the Franco-Russian accord; another was that Britain and France, already negotiating, finally patched up a fragile peace early in 1802 at Amiens. It was not expected to last long, nor did it.

When fighting broke out again in May 1803, the British government set about the laborious diplomatic task of building a new coalition of the enemies of France. Gradually the obvious candidates – Austria and Russia – were enlisted, subsidies promised, and campaigns and force contributions planned. The Baltic was involved in two ways. The British land contribution was partly to be an army in the Mediterranean, where an Anglo-Russian expeditionary force was to overrun Italy, but its main contribution, apart from at sea, was to be an expedition to Hanover. This had been overrun by French forces as soon as the new war began in 1803, but early in 1805 it became clear that the outbreak of the Franco-Austrian war had drawn off most of the French occupying forces under Marshal Bernadotte, which had a long march to reach the fighting area on the Danube. This provided a fine opportunity for a British army to recover Hanover and to pose a major threat to the whole French position in Germany and Holland. Other German states – Saxony, Hesse-Kassel – were unwilling to commit themselves to the coalition, and were actually fighting with Napoleon, but they might well change their minds when and if the British army succeeded and came close to their territories.

Into this new situation Prussia and Sweden intervened. The Swedish king, Gustav IV Adolf, was visiting his in-laws in Baden in southern Germany in 1804 when a French cavalry force kidnapped the duc d’Enghien from his quiet refuge in Baden itself. He was then executed after a swift military ‘trial’.