Where supertanker may dock by area for old weapon (3,6)
I believe the answer is:
big bertha
'old weapon' is the definition.
(nickname of German WW2 cannon)
'where supertanker may dock by area' is the wordplay.
I cannot quite see how this works, but
'dock' could be 'berth' (I've seen this in another clue) and 'berth' is located in the answer.
'area' could be 'a' (maths abbreviation) and 'a' is found in the answer.
The remaining letters 'big' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'for' is the link.
(Other definitions for big bertha that I've seen before include "Great War German gun" , "WWI German siege gun" , "cannon" .)