The most common and most likely answer to this crossword clue is the 6 plus 3 letter word DESERT RAT
I've seen this crossword clue in Financial Times
D
E
S
E
R
T
R
A
T
More clues leading to the result DESERT RAT
- Soldier to change sides twice
- Soldier or sailor turning up after leave
- Abandon reduced price for foreign jumper
- Soldier and sailor back after leave
- Soldier’s daughter retreats in confusion
- Old soldier wrongly arrested, trial’s beginning
- Soldier and sailor returning after leave
- Virtue shown by sailor, sent up by soldier
- British soldier restarted fighting
- Soldier or sailor returning on leave
Buddy explains!

The straight part
We know that "soldier" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case soldier = desert rat.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.