It is impossible to predict what a court might do in the future if the circumstances of location change. And, until you actually know for certain that you are being restationed and where, the court won't address the issue (as it would just be speculative at this juncture).
While certainly transportation and scheduling for visitation with the NCP may change substantially if you were to be transferred to the West Coast or another country, this fact in and of itself does not have to be determinitative of the custody issue. Factors in your favor would be that you (or your spouse) has been the child's primary care giver and that there are many benefits to being a military child and getting to see the world and being exposed to other cultures. If it's a reassignment to a combat zone, obviously you would not want to take the child there (I don't think the military allows family relocation into combat zones at all).
The question in a distant relocation situation will be how far can and will the custodial parent bend over backwards to ensure the child has as much contact (via email, cell phone, Skype, etc.) and vistation (at CP's expense as to travel costs) with the NCP. If you all have a very generous, well-thought out plan in place to propose to the court (which may mean things like giving the NCP every spring break, christmas break, and most of the summer every year), chances are much greater that the NCP may just agree to it without any fight or, if not, that the court will allow the relocation. It is NOT a guarantee, but it is a recommended strategy.
This response does not create an attorney-client relationship and is intended for general information purposes only.