Marine base interrupts tea for siren (7)
I believe the answer is:
charmer
'siren' is the definition.
(thesaurus)
'marine base interrupts tea' is the wordplay.
'marine' becomes 'RM' (abbreviation for Royal Marine).
'base' becomes 'e' (Euler's number - base of natural logarithms).
'interrupts' means one lot of letters goes inside another.
'tea' becomes 'char' (I've seen this before).
'rm'+'e'='rme'
'rme' going inside 'char' is 'CHARMER'.
'for' is the link.
(Other definitions for charmer that I've seen before include "One who delights others" , "relied on for a spell?" , "Smooth talker" , "One playing with snake" , "See 6" .)