12a An explosive start for British shipping...down to a result of German engineering ? (1-4)
7/8a This must follow - once out of play in GAA. (4,4)
27d It still protrudes under sealed lips.(4)
17d D d (9) Arc of a circle between first and last letter
I don't understand the DEPRESSED answer (the clue shows a large D followed by an arc to a small rounded d , I understand), but my DEBRIEFed was no better.