So, it the Navy retiree is interested in golf or wants to get into golfing, purchase him a set of golf clubs and encourage him on the same. Now that he has ample of time in his hand to do just whatever he wants, golfing could just be a great choice for him while he will really be appreciative of your thoughts and understanding.
Another time pass for retirees is fishing. Besides, being a man of the water-world, he would want to venture into the sea once in a wild and maybe to fish. This will always keep him in touch with the water. So, fishing equipments such as fishing poles will make great items for navy retirement gifts.
Keepsakes also make great gift items especially when it is an item that will remind them of their service. So, keepsakes such as Navy afghan, navy stamp art, navy retirement poems, navy blankets, etc. make great navy retirement items and will always remind them of their service in the Navy. Even a Navy keepsake box to store all the medals that he got in appreciation of his labour in the navy will be great.
Being a Navy, you could also think of a miniature of a ship, personalized it with the name of the retiree, and gift it too. Try to make a personal touch in all the gifts, if possible.