And I am going to make this comment here to state the obvious. A ship the size of the Vigilance would have not one med bay but two if not three med bays. There would be a fore and aft med bay and each would have a commander rank or above medical officer. There are likely to be a commanding officer for the medical bay and a XO in charge if the CO is not available. In my case, I would be the CO of a medical bay(most likely the aft med bay) and the XO would be a Lieutenant Commander or Lieutenant. The size of the ship and amount of people who work on it makes it so that there is most likely a hundred or so medial corpsmen and women or more. The lowest rank we can have in the medical bay would be a Hospitalman recruit and the rank above those are as follows. E-2: Hospitalman Apprentice, E-3: Hospitalman . That is just basic ranking for them. After that they are petty officers.