CSS Acadia is a former hydrographic surveying and oceanographic research ship of the Hydrographic Survey of Canada and its successor the Canadian Hydrographic Service. Acadia served Canada for more than five decades 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. Today she is a museum ship, designated as a National Historic Site of Canada, moored in Halifax Harbour at the Maritime Museum of the Atlantic.