sea duty
(1) In this section, the term “sea duty” means duty performed by a member— (A) while permanently or temporarily assigned to a ship and— (i) while serving on a ship the primary mission of which is accomplished while under way; (ii) while serving as a member of the off-crew of a two-crewed submarine; (iii) while serving as a member of a tender-class ship (with the hull classification of submarine or destroyer); or (iv) while serving as an off-cycle crewmember of a multi-crewed ship; or (B) while permanently or temporarily assigned to a ship and while serving on a ship the primary mission of which is normally accomplished while in port, but only during a period that the ship is away from its homeport.