He is thinking about a degree from UNG in History, as it contains the military science courses the school offers. There is no straight Military Science degree. In thinking that there was the possibility that he might not be able to get active duty, I don't know that he would want to pursue the history degree, because he doesn't want to be a teacher. He would probably major in Biology, with the intent to become a Physician Assistant in the civilian world and be successful in the NG or AR.
I'll keep my thoughts on your underwater basket weaving degree and scratching his way to active duty comments to myself. You know nothing about my son, his accomplishments or his potential. He doesn't want active duty to have a full time job. He wants active duty because he wants to be an officer in the United States military.
My personal advice - have your son major in something he likes -- specifically something he can see himself doing in the event a) he doesn't get AD or b) he doesn't want AD.
And as Aglahad pointed out - you can still be in the NG or Reserve and an officer at the same time.
Just stress to your son of the idea of keeping an open mind while in college (don't tunnel vision).
I know I came into ROTC this past fall fully bent on going AD. But as my interest in my major grew (firearms engineering), I sort of came to the conclusion that, if I could secure a job with someone say Magpul, BCM, or Haley Strategic (etc etc) by the time I graduate ... I might just go Guard/Reserve and spend X years there ... I would definitely be making more money than most in the Military then.
Also, one thing I didn't quite see anyone mention is ADSO'ing. It's another way to boost your chances of getting AD. ADSO stands for Active Duty Service Obligation - in essence you add an ... additional 3 years (I think) to your years in Service for something that you want (ie: post location, branch).
Furthermore, there's also BRADSO - Branch Active Duty Service Obligation. As the name implies, you extend your time in the Army for a particular branch, however this does not exist for all branches --> such as combat arms branches (ie: Infantry, Armor, Aviation). This only exists for specific branches such as Signal Corps, Chemical Corps, Corps of Engineers ... and a few others I can't think of off the top of my head. There are also several prerequisites; 1. you have to have (I think) at least a 2.75 GPA, and have a major that similarly aligns with the branch. Easy example, engineering major --> Corps of Engineer. Conversely, you can't be an engineering major and BRADSO Signal Corps.
... however with all good things, nothing lasts forever. I'm not sure how long the BRADSO program will be kept ... there's already been talk about massive overhaul of the OML model for FY15 .... at least that's what I keep hearing the MS4's say.
Just some things to also consider. Best wishes to your son in the fall!