Complex sentence: During World War I service for the United States Army Transport Service, USAT "Montanan" carried cargo and animals to France, and was in the first American convoy to sail to France after the United States entered the war in April 1917.
Split into simpler sentences: During World War I service for the United States Army Transport Service, she was known as USAT "Montanan". In World War I, USAT "Montanan" carried cargo and animals to France, and was in the first American convoy to sail to France after the United States entered the war in April 1917.