Flimsy Trident missiles are kept here, targeted primarily against Bali's interior (13)
I believe the answer is:
insubstantial
'flimsy' is the definition.
(thesaurus)
'trident missiles are kept here targeted primarily against bali's interior' is the wordplay.
'trident missiles are kept here' becomes 'insubs'.
'primarily' says to take the initial letters.
'against' becomes 'anti' (I've seen this before**).
'interior' says to take the centre.
The centre of 'bali' is 'al'.
The initial letter of 'targeted' is 't'.
'insubs'+'t'+'anti'+'al'='INSUBSTANTIAL'
(Other definitions for insubstantial that I've seen before include "Tenuous" , "Meagre" , "Lacking solidity" , "Flimsy" .)