Throughout the 1803/5 campaign, the future of Sardinia was one of Nelson's main preoccupations. At that time the island was ruled by an absentee King, Vittorio Emanuele I, with his court at Turin on mainland Italy, exercising government though a Viceroy, his brother the Duke of Genoa, who was based in Cagliari. Although a neutral state, the island was separated from French-held Corsica only by the narrow Straits of Bonafacio, and so there was constant threat of invasion.

During his initial tour of his command in 1803, Nelson decided that Malta was too far from Toulon to be useful as a base for his ships, and so he was on the lookout for somewhere closer. Sardinia offered an ideal candidate – Agincourt Sound in the midst of islands at La Maddalena, on the island's north coast, a large, sheltered and deep-water anchorage not unlike Scapa Flow. Nelson found that he could obtain wood and water there and some limited local supplies. However, its main value was that it offered a safe haven where he could unload his supply ships from Malta, effect repairs to his ships that could not be done at sea, and rest his crews. Best of all it was only 250 miles from Toulon – just over a day's sailing in the right conditions. Accordingly, Nelson decided to use La Maddalena as his main forward base. However, because Sardinia was officially neutral, he had to work hard to establish friendly contacts both with the national government and with the local inhabitants.

Very little of the correspondence resulting from these contacts found its way into Nelson's official letter-books and, as a result, his relations with Sardinia have been touched on only very sketchily in biographies. However, in 2001, 22 letters from Nelson to the King and Viceroy of Sardinia were located by John Gwyther in the State Archive in Turin – all but one of them dating from the period 1803–5. Comparison with the material in the British Library pressed copy letter-books has revealed that many of the Turin letters were copied there, which indicates that Nelson regarded them as sensitive and not for the public record.