You may want to think about calling the school and telling them that it is 2 years but maybe three.
However, I don't see why you couldn't wait until like 1.5 years from now and then request an additional deferral due to the Army constraint and if they say no, you can still just reapply to schools in that cycle. When you defer, it does not mean you can't let the time go or decline and then reapply. No need to get worked up about it if the choices are get an additional year or have to reapply.
I heard from a friend of mine at Columbia that someone had deferred at a school (I think Columbia) for like seven years! You can call and request an extension later, and as long as it is not to just sit on your behind, but for something like service, I would hope the schools would understand.