Oh, interesting facts! Thanks!
more I 've read here http://www.militaryfactory.com/ships/detail.asp?ship_id=Whiskey-Project-613-Attack-Submarine
formally, after graduation my marine school in 1988, in Vladivostock...I had minor military rank automatically, allows me to occupate pozition of comander of submarine engineering department, and as I could remember now,in the classes we study this ,613 project... very fanny it sounds now,but in those time all such kind of information was under BIG secret, for us, cadets...in the begining of the lesson,we receive books and paper ,to make notes during lessons, and after completion,need to return everithing back to duty officer!!! :)))no one piece of paper was allowed to left classroom...can You imagine?...and this was just kind of reprodaction /modification of german submarine of WW2 period...that time of couse nobody tell us real history of 613 project desighn... happy that my military dutes long time ago expiered...:)))
Good luck in building Your U21! :)
ps
as I remember ,those time, in the classroom,there was big detailed model of 613project,approx 2 mtrs long, demonstrated all existing valves ,pipes,wiring,diezels,batteries,el. motors and so on... front part ,along hull, was opened for visual excess to all machinery placed inside...this high marine school still exist,but what happendcwith that model...no idea...