Not always. It is proper to refer to Seaman Recruits (E-1),
Seaman Apprentices (E-2) and Seaman (E-3) all as Seaman. However,
there is also Fireman, Constructionman, etc. So if you are a
Seaman, Seaman Apprentice, or Seaman Recruit, then yes, you can be
referred to as Seaman.