 After UB @-@ 8 was transferred to the Bulgarian Navy in May 1916 , she was renamed Podvodnik No. 18 ( in Cyrillic : Пoдвoдник No. 18 ) . She was Bulgaria 's first submarine , and was engaged primarily in coastal defense duties off Bulgaria 's main Black Sea port of Varna . Podvodnik No. 18 survived the war and was ceded to France after the Treaty of Neuilly @-@ sur @-@ Seine . 
 After UB @-@ 8 was transferred to the Bulgarian Navy in May 1916 , she was renamed Podvodnik No. 18 ( in Cyrillic : Пoдвoдник No. 18 ) . She was Bulgaria <a href='null_genetive' title='1'><mark>'s</mark></a>first submarine , and was engaged primarily in coastal defense duties off Bulgaria <a href='null_genetive' title='2'><mark>'s</mark></a>main Black Sea port of Varna . Podvodnik No. 18 survived the war and was ceded to France after the Treaty of Neuilly @-@ sur @-@ Seine . 
After UB @-@ 8 was transferred to the Bulgarian Navy in May 1916 , she was renamed Podvodnik No. 18 ( in Cyrillic : Пoдвoдник No. 18 ) . She was Bulgaria  first submarine , and was engaged primarily in coastal defense duties off Bulgaria  main Black Sea port of Varna . Podvodnik No. 18 survived the war and was ceded to France after the Treaty of Neuilly @-@ sur @-@ Seine .