Discharge the pig-headed debtor and bring in the artillery! (9)

I believe the answer is:

firepower

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'bring in the artillery' is the definition.
I can't tell whether this defines the answer.

'discharge the pig-headed debtor' is the wordplay.
'discharge' becomes 'fire' (synonyms).
'the pig-headed' becomes 'p' (this might be a standard abbreviation of which I'm unaware).
'debtor' becomes 'ower'.
'fire'+'p'+'ower'='FIREPOWER'

'and' acts as a link.

Can you help me to learn more?

(Another definition for firepower that I've seen is " Strength available".)

I've seen this clue in the Sydney Morning Herald.

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