Did you know that the large U-boat bunkers from WW II had their origins in Flanders in WW I ?

Submarines were much more important in WW I then in WW I which is most of the time forgotten. Also completely forgotten is the fact that the large U-boat bunkers as they were constructed in WW II at Hamburg or for example Saint-Nazaire, had their origins in those constructed in Flanders during the Great War.

Here's an example of one in the Brugge/Brugse harbour in 1918