Royal Caribbean offers military discounts to active, reserve and retired members of the U.S. military and the Canadian Forces. Qualifying military personnel must present a photocopy of current military ID at the time of booking.
Recently, on the RCI Cruise Critic message board, there was a lengthy discussion regarding RCI's military discount policy. I swear someone said that they called RCI and eventually got customer service to understand that not all veterans are retired and that the discount applied to honorably discharged vets who had served a minimum of two years. Those vets would have to show their DD 214. I'm a 6 year vet and always look for those kinds of discounts. I still haven't found one on RCI yet.