Low attack involving Northern Line (8)

I believe the answer is:

monorail

I'm a little stuck... Click here to teach me more about this clue!

'line' is the definition.
(type of railway line)

'low attack involving northern' is the wordplay.
'low' becomes 'moo' (both can mean to make a cow noise).
'attack' becomes 'rail' (I can't explain this - if you can you should give a lot more credence to this answer).
'involving' is an insertion indicator.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'moo'+'rail'='moorail'
'moorail' enclosing 'n' is 'MONORAIL'.

Can you help me to learn more?

(Other definitions for monorail that I've seen before include "Suspended railway" , "Hanging transport system" , "Form of transport" , "train" , "Type of railway" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.