Type of missile launched originally is found in sea (9)
I believe the answer is:
ballistic
'type of missile' is the definition.
'launched originally is found in sea' is the wordplay.
'originally' says to take the initial letters.
'found in' is an insertion indicator.
'sea' becomes 'baltic' (Baltic is an example**).
The initial letter of 'launched' is 'l'.
'l'+'is'='lis'
'lis' put into 'baltic' is 'BALLISTIC'.
(Other definitions for ballistic that I've seen before include "Projectile" , "Winsome deer" , "To do with the flight of projectiles - basic lilt (anag)" , "Moved by gravity" , "Like missiles" .)