You were given the chance to enter it but you missed it. Go back to My Info and click edit by his name. Then go through the screens more slowly and carefully until you see the one where you can say he was active duty military.
There will be a question about what he did for a living and it will ask if he served in the U.S. Armed Forces.....
Click yes
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**