Liam,

I looked through some additional material last night. The good news is that should be possible to determine which U-boat -- if any -- sank Keeper. UC 66 is the only U-boat that went missing in early June, and can probable be eliminated as a possibility.

U-boat war diaries (KTBs) have survived and are available on microfilm, so it's just a question of looking to see if one of these boats attack a smallish merchant ship along the west coast of Ireland on June 10 - 13. If there's no match, we are left with either a mine or a marine casualty of some sort. Unfortunately, I only have have a minority of the KTBs, though will be acquiring more over time. I will check a few of the more obvious possibilities over the weekend.

It is not a given that an U-boat would have sunk Keeper by gunfire or scuttling thou certainly possible. The propensity to use the deck gun varied by commanding officer, some were very fond of it, other would use it against only the smallest targets. Perception mattered too -- it was very easy to misestimate the size of a ship. The most extreme case I have seen is from the Irish Sea in March 1918, were an U-boat put a torpedo into a 157 grt steamer. The attack happened at night, and the submarine's CO estimated her to be a 3000 tonner...

Best wishes,

Michael