Martin,

This does get complcated very fast as U-boat gun armament is sort of a moving target. Boats were rearmed during the war, and it’s difficult to know the exact sort of armament (gun and mount) fitted to any particular boat at any particular time. That said, early UBII class boats like UB 18 were originally fitted with 50mm guns and then upgunned to 88mm weapons in fall 1916.

There’s at least one assumption that’s likely to be problematic though: That the gun came off of UB 18. The original Royal Navy sinking claim for UB 18 was on November 17, 1917 at about 50°08'N, 3°42'W by mine. There’s one problem with this: The U-boat mined was UC 51, not UB 18.

UB 18 is now believed to have been rammed and sunk by a trawler in RN service on December 9, 1917 at 49°17'N, 5°47'W, though I would take that position as being very approximate.

It would help to know the location from which the gun was brought up. Possible sources are not necessarily limted to war losses — a number of boats were lost postwar while under Royal Navy control in the English Channel.

Best wishes,
Michael Lowrey
uboat.net