for the entry uc 21 on this website it states this:

30 Sep, 1917 - Departed Zeebrugge for the Bay of Biscay on 13.9. Lost by unknown cause on or after Sept. 16, 1917. 27 dead (all hands lost).

I think this may corelate with an attack made on a u boat on the 29th september.

In the book u boat hunters by Peter London, page 31 it gives this account (here shortend) while patrolling between Lizard and Eddystone lighthouse on the 29th sept 1917, Coast Class c-9 sighted disturbance of sediment east of Eddystone. c-9 called up two armed trawlers and itself dropped a 100 lb bomb at the head of the trail and the trawler CV 567 released two depth charges resulting in oily track and bubbles. further depth charges dropped resulting in greater discharge of oil and bubbles from a stationary position. Trawler marked position with a buoy and went to fetch more depth charges, returning later with two further trawlers and a destroyer. two more depth charges dropped resulting in more oil rising to the surface. all units agreed that the u boat had probably been destroyed and left.

Unfortunately a precise location is not given.

I think this may have been the final fate of uc 21, what do you think????

Rob