Again the armed aircraft is protecting the ship (9)
I believe the answer is:
freighter
'ship' is the definition.
(freighter is a kind of ship)
'again the armed aircraft is protecting' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'the armed aircraft' becomes 'fighter' (fighter is a kind of aircraft. I am not sure about the 'armed' bit.).
'is protecting' indicates putting letters inside (inserted letters are held or protected).
're' going inside 'fighter' is 'FREIGHTER'.
'the' is the link.
Can you help me to learn more?
(Other definitions for freighter that I've seen before include "transport vessel" , "Cargo-ship" , "Cargo ship" , "Cargo-carrying ship or plane" , "A plane carrying large load" .)