U-boat has means to make tunnels underground (7)
I believe the answer is:
subways
'to make tunnels underground' is the definition.
I can't tell whether this defines the answer.
'u-boat has means' is the wordplay.
'u-boat' becomes 'sub' (German submarine).
'has' is a charade indicator (letters next to each other).
'means' becomes 'ways' (I've seen this in other clues).
'sub'+'ways'='SUBWAYS'
Can you help me to learn more?
(Other definitions for subways that I've seen before include "Underground passages" , "Pedestrian tunnels" , "transport systems" .)