The most common and most likely answer to this crossword clue is the 12 letter word ARTILLERYMAN
I've seen this crossword clue in The Times
A
R
T
I
L
L
E
R
Y
M
A
N
More clues leading to the result ARTILLERYMAN
Buddy explains!
The straight part
We know that "Someone working in an army, possibly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case someone working in an army, possibly = artilleryman.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 ARTILLERYMAN mean?
ARTILLERYMAN noun- A soldier enlisted in an artillery unit or who uses artillery.