Alloy rises to top of forge, creating flotillas (6)
I believe the answer is:
fleets
'flotillas' is the definition.
(I've seen this in another clue)
'alloy rises to top of forge' is the wordplay.
'alloy' becomes 'steel' (steel is a kind of alloy).
'rises' says the letters should be written backwards.
'to' says to put letters next to each other (I've seen this in other clues).
'top of' indicates taking the first letters.
The first letter of 'forge' is 'f'.
'steel' backwards is 'leets'.
'leets' put after 'f' is 'FLEETS'.
'creating' acts as a link.
(Other definitions for fleets that I've seen before include "armadas" , "Groups of vehicles or vessels" .)