Agreed Malone.
17a School has short novel about a Royal Navy battleship sunk in 1943 (11)
A: Scharnhorst.
Annoying obscure general knowledge but that aside, I can't fully parse it.
School = sch, a Royal Navy = arn, which leaves the bit I can't see, how does horst = short novel?
12d Their vessel transport army material (11)?
A: shirtsleeve.
What's this got to do with army material, doesn't the answer refer to anyone wearing a shirt without a jacket? And is it one word?