Complex sentence: In October of that year he was formally appointed commander-in-chief of the Leeward Islands station, and within the first three months of 1762 had reduced the important island of Martinique, while both St Lucia and Grenada had surrendered to his squadron.
Split into simpler sentences: In October of that year he was formally appointed commander-in-chief of the Leeward Islands station. Within the first three months of 1762 had reduced the important island of Martinique, while both St Lucia and Grenada had surrendered to his squadron.