Seaman attains objectives (7)
I believe the answer is:
targets
'objectives' is the definition.
('target' can be a synonym of 'objective')
'seaman attains' is the wordplay.
'seaman' becomes 'tar' (Jack Tar is an informal term for a sailor).
'attains' becomes 'gets' (I've seen this in another clue).
'tar'+'gets'='TARGETS'
(Other definitions for targets that I've seen before include "Butts" , "Goals" , "objectives of firing people" , "Aim points" , "Reference points to shoot at" .)