Some positions are not the standard ship DH positions. Some are outside the normal roster, such as Chief of Operations, or Chief Tactical Officer.

Often in these positions there are no rostered player character junior officers for the Department Head to manage, but this is not to say your duty to the ship is over. You still should keep yourself busy and help out in the sim where required. For example, you can create Nameless Ensign Junior Officers to give tasks to IC. Remember to support your command staff and prove that you can perform in the position. Be an asset to the ship and the crew.