The most common and most likely answer to this crossword clue is the 13 letter word DEREQUISITION
I've seen this crossword clue in The Times
D
E
R
E
Q
U
I
S
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T
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O
N
Buddy explains!

The straight part
We know that "return to civilian employment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case return to civilian employment = derequisition.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DEREQUISITION mean?
DEREQUISITION verb- To return or release (something previously requisitioned).