In May 1803, the fragile Peace of Amiens shattered and war broke out again between Britain and France. Even before hostilities began, Nelson was appointed Commander-in-Chief of the Mediterranean. At forty-four, he was the youngest man ever to hold that important post, and he was chosen over the heads of senior and more experienced admirals – including Lord Keith, who had held the command at the end of the previous war and who had expected to be appointed again.

Having hoisted his flag on board HMS Victory on 18 May 1803, Nelson sailed three days later, arrived at Gibraltar on 3 June and, after making a quick tour of his command, joined his new squadron off Toulon on 8 July. From then, until he left the Mediterranean on 6 May 1805, in pursuit of the French Toulon fleet under Vice Admiral Pierre de Villeneuve, his whole attention was taken up with conflicting demands of this most complex of commands, and he carried out his duty without relief, and with no breaks for leave. A remarkable achievement, both of personal stamina and professional ability, it has been dealt with by most of Nelson's biographers as if it was simply a long and rather tedious prelude to the more dramatic and exciting Trafalgar campaign. This view is completely turned on its head by the important new evidence presented in this section. We can now see that it was by far the most important period in his professional career, during which he demonstrated his abilities as an all-round commander better than at any other time.

Our understanding of his achievement has been greatly enhanced by the most important single discovery during the recent research: the treasure-trove of unpublished letters contained in the nine volumes of Nelson's pressed copy letters for this period, now in the British Library. These letters illuminate areas not covered adequately before in any biography, such as Nelson's wide-flung intelligence network, or his secret dealings with the Kingdom of Sardinia. Additionally, the location of complete ‘runs’ of personal letters to Prime Minister Henry Addington, the Duke of Clarence and First Lord of the Admiralty Lord Melville enable us to show Nelson's thought processes more clearly than ever before.