Which early-twentieth-century ocean liner that served in the Second World War most deserved a long postwar career?
Short answerQueen Mary, which did enjoy a postwar career and survives at Long Beach, though her preservation has not always been easy.
NotesQueen Mary is the choice, with the caveat that she was built in 1936 and survived well beyond the proposed period. Her war service and later survival place her slightly outside the question's 1910s-to-1930s frame. Her preserved status at Long Beach gives the answer a heritage dimension as well as an operating-history one. Her treatment also warns that preservation does not guarantee consistently good stewardship of a historic ship.