Complex sentence: Beginning in February 1940, she mainly served along the U.S. east coast and in the Caribbean area, but made one trans-Atlantic round-trip voyage in mid- 1940, rescuing the Norwegian Crown Princess and many other persons from the European war zone.
Split into simpler sentences: Beginning in February 1940, she served primarily along the U.S. east coast and in the Caribbean area. She made one trans-Atlantic round-trip voyage in mid- 1940, rescuing the Norwegian Crown Princess and many other persons from the European war zone.