Yes I have considered a career in either the Navy or army for quite a while now. Although being on a leisure cruise ship and a war ship, differs greatly. You are not catered for hand and foot by the crew and you will soon find out that it's far from a relaxing voyage when you're sailing towards a war zone. If you want to get more of an opinion about a life in the Royal Navy, you could watch the channel 4 series, Royal Navy school. It'll give you a basic idea of what you will be going through in basic training. I'm not an expert, but I've been researching this sort of thing for a few months now as I myself am in the crossroads of where to go next. Just ask if you have any more questions, I've got a good chance of helping you out.