Rear Admiral Callo is a historian and writer. His books include Nelson in the Caribbean: The Hero Emerges, 1784-1787 (Naval Institute Press, 2003); Nelson Speaks: Admiral Lord Nelson in his own Words (Naval Institute Press, 2001); and Legacy of Leadership: Lessons from Admiral Lord Nelson (Hellgate Press, 1999). Admiral Callo is also the co-author of Who's Who in Naval History: From 1550 to the Present (Routledge, 2004) and contributed an essay to The Trafalgar Companion (Osprey Publishing, 2005).