Rob,

Not so simple. I'm working on a book on WWI submarine losses and to really answer your question would take about 10,000 words.

The brief version is that virtaully all WWI U-boat losses have something listed as being responsible for their loss. Now whether that something is correct is another question entirely -- most attribution come from the Royal Navy 1919 and are often based upon an incomplete understanding of U-boat operations (when specific bats sailed and their assigned patrol areas).

Also, British sinking claims can be exaggerated, with the common secondary source versions often containing details not included in the logs of the vessels involved.

There are a limited number of missing U-boats or U-boats with suspect sinking claims that might have come near the Cornwall coast. UC 66 is the most obvious case. January 1918 in general is of interest. Beyond that, UB 18, UB 29, UB 32, UB36, UB 104, UB 113, UC 19, UC 21, and UC 72 might be of interest. Practically speaking, the list is shorter than that because of as yet unidentified sub wrecks that have been found elsewhere.

It's possible to attribute out specific actions. I wouldn't call it simple, but it's doable. Basically, you describe the action in as much detail as possible (date, time, location) and then those of use with the appropriate resources can determine which boats were at sea. The next step would be to look at Spindler's official history, and after the U-boat KTBs.

Best wishes,
Michael