Is he the first to do the firing on board? (7,6)

'do the firing on board?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'is he the first' is the wordplay.
I cannot quite see how this works, but
'he' could be 'ker' and 'ker' is present in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'first' could be 'leading' (leading can mean first or main) and 'leading' is found in the answer.
The remaining letters 'so' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'to' is the link.

Can you help me to learn more?