Soldiers in camp - sorry, on manoeuvres (4,5)
I believe the answer is:
'soldiers in' is the definition.
The definition suggests a singular noun which matches the answer.
'camp sorry on manoeuvres' is the wordplay.
'on manoeuvres' indicates an anagram (the letters manoeuvre into a new form).
'campsorry' is an anagram of 'ARMY CORPS'.
Can you help me to learn more?
(Another definition for army corps that I've seen is " Military unit".)