Ammunition to haul on board (5)
I believe the answer is:
slugs
'ammunition to' is the definition.
I can't tell whether this defines the answer.
'haul on board' is the wordplay.
I cannot quite see how this works, but
'haul' could be 'lug' (I've seen this before) and 'lug' is found in the answer.
'on board' could be 'ss' (I've seen this in other clues) and 'ss' is located in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for slugs that I've seen is " Land molluscs".)