Career Progression: Masters or No

SGT Thayer hit it on the head. There is NO REQUIREMENT for a Masters degree. Period. That being said, You want to stand out from your peers in a POSITIVE way. 

Sir, I am not particularly adept on the Officer side of things, but look at it this way: You are competing with your peers for assignments, promotions, etc. If you are planning on making the military a career and you and one of your peers both get looked at to make Major, Lieutenant Colonel, so on and so forth, both of you have the same experience in everything, why would they pick you to get promoted if your peer has a Masters Degree? It shows you that you are trying to better yourself as a well rounded individual. In my opinion, a Masters Degree for a field grade Officer and higher is a must. Just my two cents.

I suggest one might worry not about career progression but rather about knowledge that can permit one to serve more effectively and contribute more to the service and the nation. And if that is useful in one's career (and most likely it will be) then all the better. In my experience the better educated soldier stands out when compared with peers not by the added letters after one's name (like MBA) but rather by their ability to take on complex jobs and create flexible solutions. When I was an undergraduate my class had a motto; "Knowledge in youth becomes wisdom with age". As one's knowledge deepens and the concepts one is exposed to broadens, they are able to do more and contribute more. It probably begins to show up in the mid-grades as you are called on to address more complex staff work for which there are no text book solutions. I do think the degree field is important and there are plenty of fields that have direct application.