Complex sentence: His military skills enabled him to obtain, in 1764, promotion to Assistant Major of the Hibernia Regiment and, in 1773, while serving in Pamplona, Spain, O'Neill obtained the rank of Captain of the regiment.
Split into simpler sentences: His military skills enabled him to obtain, in 1764, promotion to Assistant Major of the Hibernia Regiment. In addition, in 1773, while serving in Pamplona, Spain, O'Neill obtained the rank of Captain of the regiment.