Provide weapons for Royal Marines following note (3)
I believe the answer is:
arm
'provide weapons for' is the definition.
(I've seen this before)
'royal marines following note' is the wordplay.
'royal marines' becomes 'rm'.
'following' says to put letters next to each other.
'note' becomes 'a' (musical note).
'rm' after 'a' is 'ARM'.
(Other definitions for arm that I've seen before include "Body part" , "Authority" , "Maybe rifle" , "ready for war" , "Equip with weapon" .)