Craft about to change (1-4)
I believe the answer is:
u-boat
'craft' is the definition.
(U-boat is an example)
'about to change' is the wordplay.
'to change' indicates anagramming the letters.
'about' anagrammed gives 'U-BOAT'.
(Other definitions for u-boat that I've seen before include "Submersible warship of WWII" , "Sea vessel" , "German wartime submarine" , "Submersible warship armed with torpedoes" , "Take pool exercise" .)