Informed state of Royal Engineers in Swansea on manoeuvres (9)
I believe the answer is:
awareness
'informed state' is the definition.
'royal engineers in swansea on manoeuvres' is the wordplay.
'royal engineers' becomes 're'.
'in' means one lot of letters goes inside another.
'on manoeuvres' indicates an anagram (the letters manoeuvre into a new form).
'swansea' anagrammed gives 'awaness'.
're' put within 'awaness' is 'AWARENESS'.
'of' is the link.
(Other definitions for awareness that I've seen before include "Grasp" , "Knowledge or consciousness" , "understanding" , "Knowing" , "Knowledge (of a fact)" .)