Engaged in war, Madagascan navy (6)
I believe the answer is:
armada
'navy' is the definition.
(I've seen this before)
'engaged in war madagascan' is the wordplay.
'engaged in' says the answer is hidden in the clue.
'ARMADA' can be found hidden inside 'war madagascan'.
(Other definitions for armada that I've seen before include "Large Spanish fleet" , "Old Spanish fleet" , "Naval fighting force" , "A great fleet, ships or planes" , "vessels" .)