I see where the confusion is...when you are "applying" from ROTC (and probably the other commissioning sources as well) you must fill out an ordered preference for every option.
However, when applying to the Active Duty Rated Board (ie you are already commissioned), you are NOT required to do so (see my previous explanation).
So blake, after reading your question again, it's rather vague if you are speaking about applying from ROTC or as a commissioned officer trying for a rated spot. Either way, your question should have been answered in some fashion.
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