According to this reference site:
https://uboat.net/wwi/types/shipyards.html
Most of the german u-boats in WWI were constructed in 5 shipyards (in 4 cities):
A.G. Weser, Bremen (81)
Blohm & Voss, Hamburg (89)
Germaniawerft, Kiel (84)
Kaiserliche Werft, Danzig (46)
Vulcan, Hamburg (69)
However in the game in 1916 scenario when you can build subs squadrons, it is possible in 3, the 3 in green in the map with the structures are:
Bremen (city, harbor, depot).
Stettin (city, depot, harbor, shipyard).
Danzig (city, depot, fort, naval base).
It is true that in 1914 when only coastal subs can be built, Kiel and Hamburg are also available, the structures inside are:
Kiel (city, depot, fort, naval base).
Hamburg (city, depot, trade port).
In the other 3 the structures are the same.
So the question is, which structure controls the u-boats construction? Cannot be the city+depot! The only coincidences in structures of the 3 or 5 cities in both scenarios.
Besides Hamburg and Kiel, where most were built, are missing in the game in 1916 and the construction of course continued there. On the other hand, Stettin was not historically relevant for u-boats and is present in both scenarios, and it is the only city where a shipyard is?
How this could be improved?