The most common and most likely answer to this crossword clue is the 5 letter word REARM
I've seen this crossword clue in The Guardian
R
E
A
R
M
More clues leading to the result REARM
- Give more weapons back — one thousand
- Cultivate source of munitions — and do so again?
- Raise millions to provide new tanks, say
- Last maiden to prepare for a new engagement?
- Prepare to fight again behind military leader
- Raise male, ready for new conflict
- Prepare to fight again behind leader of militia
- Again supply weapons to attention-grabbing marines?
- Raise money to equip with new weapons
Buddy explains!

The straight part
We know that "prepare for a new engagement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case prepare for a new engagement = rearm.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 REARM mean?
REARM verb- To replace or restore the weapons or arms of a previously defeated, or disarmed army, country, person or other body.