Warnings unfortunately about the Marines (6)
I believe the answer is:
alarms
'warnings' is the definition.
(I've seen this before)
'unfortunately about the marines' is the wordplay.
'unfortunately' becomes 'alas' (I've seen this before).
'about' means one lot of letters goes inside another.
'the marines' becomes 'rm' (abbreviation for 'Royal Marines').
'alas' placed around 'rm' is 'ALARMS'.
(Other definitions for alarms that I've seen before include "Disturbs" , "Flaps" , "Scares, hopefully burglars" , "Frightens and startles" , "Danger signals" .)