While I somewhat enjoyed the task of deciphering and tracking down the myriad of specialized, arcane and obsolete words employed by Patrick O'Brian in his majestic Aubrey-Maturin series, the discovery of this book provided a much more concise and handy way of doing this.O'Brian's vast vocabulary and vast knowledge of seagoing nomenclature as well as late 18th and early 19th century social mores is impressive. This book allows one to appreciate the level of scholarship applied by O'Brian. However, this is much more than a simple glossary. It includes short biographies of leading personages of the day, histories of important battles, diagrams of ships and rigging and geographical references.While one can probably get along without this book; assuming one has access to a good dictionary, encyclopedia and other reference books, this tome certainly eases the task.