Its launchers hope it will sink (7)
I believe the answer is:
torpedo
'sink' is the definition.
(I've seen this in another clue)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for torpedo that I've seen before include "fish you want" , "Such as could sink" , "Explosive missile from submarine" , "electric ray" , "To wreck" .)