The most common and most likely answer to this crossword clue is the 9 letter word ARMAMENTS
I've seen this crossword clue in The Guardian
A
R
M
A
M
E
N
T
S
Buddy explains!

The straight part
We know that "Munitions" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case munitions = armaments.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 ARMAMENTS mean?
ARMAMENTS noun- A body of forces equipped for war.
- All the cannon and small arms collectively, with their equipments, belonging to a ship or a fortification.
- Any equipment for resistance.
- The process of building up military capacity.