Decmay Thanks for the information.I didn't expect to receive a response in such a short time.
I have photos of the medal and will try to post them, but it is a US Lines issued medal, not a Merchant Marine award. The reverse is lettered "for courageous and meritorious action in the performance of duty" and engraved with his name and the date November 17, 1955. I'm sorry I didn't post that in my original post but I did not have the medal at hand.
It would appear this is not a generic retirement award, and I would guess the date is the day of the action which earned him the award. I've been unable to come up with any notable at-sea events for that day.