"Thresher’s" 11th war patrol (this one under command of Duncan C. MacMillan, Class of 1926) took her to the South China Sea south of Formosa. While cruising on the surface on 10 January 1944, "Thresher" sighted a pair of masts, low on the horizon, and quickly dove to avoid possible detection. Coming to periscope depth soon thereafter, she approached cautiously, keeping in mind the ship may have been the advance screen of a convoy. The contact proved to be a 150-ton trawler. "Thresher" battle-surfaced, commencing fire at ; the trawler sank after "Thresher" expended 45 shells, 1,000 rounds of .50 cal (12.7 mm); and 770 rounds.