I received the following data on U-1 thru U-6 on where they were built. I can only find Docks 1 thru IV, Building Slips 1, 2 and 3 and then docks V and VI. Can you please help me understand where these building slips were located?

Thank you very much

U-Boote U 1 DWK, Helling 117a rechts
II A U 2 DWK, Helling 117b rechts
II A U 3 DWK, Helling 117b links
II A U 4 DWK, Helling 117a links
II A U 5 DWK, Helling 117c links
II A U 6 DWK, Helling 117c rechts