Complex sentence: She subsequently returned to her homeport to be refitted and then, beginning in July 1972, Intrepid participated once again in NATO exercises, visiting Copenhagen, Rotterdam, Bergen, Brussels, Portsmouth and Gourock.
Split into simpler sentences: She subsequently returned to her homeport to be refitted. Then, beginning in July 1972, "Intrepid" participated once again in NATO exercises, visiting Copenhagen, Rotterdam, Bergen, Brussels, Portsmouth and Gourock.