He was afterwards made a cornet in the Royal Horse Guards by the influence of his uncle the Duke of Richmond, and for the first time did actual military duty in this regiment, but he soon accepted Sir John Moore's suggestion that he should exchange into the 52nd, which was about to be trained at Shorncliffe Army Camp.
[1] He served in Denmark, and was present at the engagement of Koege (Køge)[2] and, his regiment being shortly afterwards sent to Spain, took part in the retreat to Corunna, the hardships of which permanently impaired his health.
After taking part in the pursuit of Masséna after he left the lines of Torres Vedras, he and his brother George were recommended for a brevet majority.
After a short stay at home he again joined his regiment at the Pyrenees, and secured the most strongly fortified part of Soult's position at the Nivelle.
As could not live on a Major's half-pay with a wife and family, he decided to become an artist, taking a house in Sloane Street, where he studied with George Jones, the academician.
The Duke of Wellington himself gave him much assistance, and handed over the whole of Joseph Bonaparte's correspondence captured at the battle of Vittoria; this was all in cipher, but Mrs Napier discovered the key.
Napier's friends actually invited to become the military chief of a national guard to obtain reforms by force of arms, which he refused on the ground that he was in bad health and had a family of eight children.
He was working on proposals for a complete scheme of reform in the government of the island, upsetting many people in the process,[6] when his tenure came to an end.
While he was at Guernsey his brother Charles had conquered Sindh, and the attacks made on the policy of that conquest led to William Napier again to write.
[7] The Encyclopædia Britannica Eleventh Edition considered his military history, at the time, to be "incomparably superior to any other English writer", comparing him to three other soldier-writers: Thucydides, Julius Caesar and Enrico Caterino Davila.