 During this stay he befriended Lt (later Lt Col) Samuel Twentyman of the 18th Regiment.In the autumn of 1779 Archibald was promoted to Major, and Twentyman joined his regiment in sailing to the West Indies.In 1779/1780 Archibald spent much time in St. Lucia in the West Indies and together with several thousand others (many of whom died) caught a fever (generally called St.Lucia Fever), after which his disposition changed greatly, to the concern of all his family.