Large amount coming in to replenish a small fleet (8)
I believe the answer is:
flotilla
'small fleet' is the definition.
(I've seen this in another clue)
'large amount coming in to replenish a' is the wordplay.
'large amount' becomes 'lot' (a lot of something).
'coming in to' indicates putting letters inside.
'replenish' becomes 'fill' (I've seen this before).
'lot' going into 'fill' is 'flotill'.
'flotill'+'a'='FLOTILLA'
(Other definitions for flotilla that I've seen before include "Fleet of small craft" , "collection of vessels" , "number of small ships" , "Group of small craft" , "set of boats" .)