 U @-@ 3 's design was an improved version of Germaniawerft 's design for the Imperial German Navy 's first U @-@ boat , U @-@ 1 , and featured a double hull with internal saddle tanks . The Germaniawerft engineers refined the design 's hull shape through extensive model trials . 
 U @-@ 3 <a href='null_genetive' title='1'><mark>'s</mark></a>design was an improved version of Germaniawerft <a href='null_genetive' title='2'><mark>'s</mark></a>design for the Imperial German Navy <a href='null_genetive' title='3'><mark>'s</mark></a>first U @-@ boat , U @-@ 1 , and featured a double hull with internal saddle tanks . The Germaniawerft engineers refined the design <a href='null_genetive' title='4'><mark>'s</mark></a>hull shape through extensive model trials . 
U @-@ 3  design was an improved version of Germaniawerft  design for the Imperial German Navy  first U @-@ boat , U @-@ 1 , and featured a double hull with internal saddle tanks . The Germaniawerft engineers refined da design  hull shape through extensive model trials .