Complex sentence: Martin was commissioned as a second lieutenant in the First Regiment of the United States Artillery and he served mainly on the northern coast, on the frontier of Maine, in the Aroostock War, and in the coastal survey.
Split into simpler sentences: Martin was commissioned as a second lieutenant in the First Regiment of the United States Artillery. He served mainly on the northern coast, on the frontier of Maine, in the Aroostock War, and in the coastal survey.