Complex sentence: He returned in the frigate "United States" in 1844 and served in "St. Mary's" in the Gulf of Mexico from 1844 to 1846; participating in operations at Galveston, Corpus Christi, Brazos, Resaca, and Vera Cruz.
Split into simpler sentences: He returned in the frigate "United States" in 1844 and served in "St. Mary's" in the Gulf of Mexico from 1844 to 1846. He participated in operations at Galveston, Corpus Christi, Brazos, Resaca, and Vera Cruz.