Complex sentence: He became commanding officer of the frigate HMS "Melampus" in 1794, commanding officer of the third-rate HMS "Defence" later in 1794 and commanding officer of the second-rate HMS "Glory" in 1799.
Split into simpler sentences: He became commanding officer of the frigate HMS "Melampus" in early 1794. He went on to be commanding officer of the third-rate HMS "Defence" later in 1794 and commanding officer of the second-rate HMS "Glory" in 1799.