Nerys Ghemor wrote:
In the real-life military, there is a difference between being an officer of the line versus a specialized officer (such as medical or JAG--referred to in the Air Force as a "professional" officer).
One example of this is that in TNG, Dr. Crusher is a full commander, but with only one exception, she is not seen to take command, and if she does pull rank, it's normally restricted to a medical context under her powers as CMO.
By the description in the article, it might be that Sisko has sometimes been an officer of the line, and sometimes not--but even that article makes clear that sometimes the distinction is blurred.
One exception to this, in the Navy, is command of medical ships, which does go to Captains of the Medical Corps. So Dr. Crusher's command of a science vessel does have precedence in real life.