CSS Acadia is a former hydrographic and oceanographic research ship of the Hydrographic Survey of Canada and its successor, the Canadian Hydrographic Service. Acadia for 56 years from 1913 to 1969, charting the coastline of almost every part of Eastern Canada including pioneering surveys of Hudson Bay. She was also twice commissioned into the Royal Canadian Navy (RCN) as HMCS Acadia, the only ship still afloat to have served the RCN in both World Wars. The ship is also the last remaining ship afloat that was present at the 1917 Halifax Explosion. The ship is now a museum ship, designated as a National Historic Site of Canada, moored in Halifax Harbour at the Maritime Museum of the Atlantic.