Hostile incursions where the fleet lies at anchor? (7)
I believe the answer is:
inroads
'hostile incursions' is the definition.
(I've seen this before)
'at anchor?' is the wordplay.
'at' becomes 'in' (synonymous in some cases - eg at school, in school).
'anchor?' becomes 'roads' (I can't justify this - if you can you should believe this answer much more).
'in'+'roads'='INROADS'
'where the fleet lies' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for inroads that I've seen before include "Sad iron (anag.)" , "Ordains as offensives" , "large quantities consumed when these are made" , "Progress" , "advances" .)