Former President working with sailors (7)
I believe the answer is:
jackson
'former president' is the definition.
(Andrew Jackson, 7th US president)
'working with sailors' is the wordplay.
'working' becomes 'on' (on can mean working or activated).
'with' is a charade indicator (letters next to each other).
'sailors' becomes 'jacks' (jack can informally mean a sailor).
'on' put after 'jacks' is 'JACKSON'.
(Other definitions for jackson that I've seen before include "American painter, 1912-56" , "American hero" , "Seventh US president Andrew - actress turned politician Glenda - singers Michael and Janet etc" , "See 13" , "Mississippi capital and 7th US president" .)