Wikipedia article on Bruge
Bruge was once one of the great commercial cities of Europe. What I did not realise until today was that it was also the location of a World War One German U-boat base. This was particularly surprising because Bruge is 14km from the coast. This map explains the geography.
A canal connects Bruge to its port of Zeebrugge. The Germans kept the U-boats in pens in Bruge, outside the range of British naval guns. The torpedo armed boats [type UB] and the mine laying boats [type UC] were built in Germany then shipped in kit form by rail to be assembled in Belgium.
The boats then travelled down the canal to Zeebrugge and out to the sea to lay mines and torpedo British ships, mainly in the North Sea.
They did that very effectively. By the end of the war they had sunk a total of 2,554 Allied ships with a total tonnage of 2.5 million.
British anti-submarine warfare improved and by the end of the war 80% of the Bruge boats had been sunk. Crews were understandably not keen on suicide missions and by 1918 some crews were either surrendering very easily or interning themselves in neutral countries.
If you would like to know more this book has just been published and this article is worth reading.