Complex sentence: Drummond also saw service in the Mediterranean and the West Indies 1805, a mere 33 years old, Drummond had attained the senior rank of major-general and was well on his way to an extremely promising military career.
Split into simpler sentences: Drummond also saw service in the Mediterranean and the West Indies. In 1805, a mere 33 years old, Drummond had attained the senior rank of major-general and was well on his way to an extremely promising military career.