Complex sentence: She returned to Yokohama on 20 February 1946, and Shanghai on 27 February; but, on 4 March, steamed from that port for the United States and arrived at San Francisco on 21 March.
Split into simpler sentences: She returned to Yokohama on 20 February 1946, and Shanghai on 27 February. Then on 4 March, steamed from that port for the United States and arrived at San Francisco on 21 March.