Fuss about rapier regularly used as weapon (7)
I believe the answer is:
torpedo
'weapon' is the definition.
(weapon used at sea)
'fuss about rapier regularly used' is the wordplay.
'fuss' becomes 'todo' (both can mean a commotion).
'about' indicates putting letters inside.
'regularly used' indicates alternate letters (letters selected on a regular basis).
The alternating letters of 'rapier' are 'rpe'.
'todo' going around 'rpe' is 'TORPEDO'.
'as' is the link.
(Other definitions for torpedo that I've seen before include "Self-propelled submarine weapon" , "Missile form a submarine" , "To wreck" , "Trooped off with underwater missile" , "Trooped (anag.)" .)