There was a discussion a little while ago about who was eligible. Carnival requires you to send a copy of your identification card to them. The card can be active duty, reserves or retiree. Also you can book 3 cabins with your military id.
Mu wife and I used the Military discount on our upcoming cruise. However, it is my son who is in the Military. There was really no problem in getting the discount. All I had to do was have my son fax a copy of his I.D. with his Drivers license. Worked for us. We go a nice discount. Good luck.
I checked into this for the New Year's Cruise we are booked on. My son is in the Army Reserves. Carnival had the holiday cruise dates blacked out for this type of discount. I'm sure it fills without them having to offer any discounts.
We just booked a 7 day on the Carnival Inspiration May 16 with a military discount. Price per person with port and taxes included was $571.90 for a 6A Guarantee. Needless to say we were floored. Great price booked directly with Carnival. We did talk to a TA here local who quoted the same price.
Last word is that there is anew policy. Retiree's only get the discount on their room rather than theirs +1. Just thought you might want to know. Also I understand this is an ever changing policy so you milage may vary!
Don't forget to check other discounts, too. We found that our cruise contact was able to get us a better deal than the military discount. We have had great luck with our military....especially with the Disney cruiselines and the ship and shore packages.