 The first Type UB I to enter service was UB @-@ 10 , which formed the nucleus of the Flanders Flotilla , on 27 March 1915 . By the end of April five more Type UB I boats had become operational . UB @-@ 10 was eventually joined in the Flanders Flotilla by UB @-@ 2 , UB @-@ 4 , UB @-@ 5 , UB @-@ 6 , UB @-@ 12 , UB @-@ 13 , UB @-@ 16 , and UB @-@ 17 ; of these , only UB @-@ 2 made the journey to Flanders by sea rather than rail . 
 The first Type UB I to enter service was UB @-@ 10 , which formed the nucleus of the Flanders Flotilla , on 27 March 1915 . By the end of April five more Type UB I boats <a href='been_done' title='1'><mark>had</mark></a> become operational . UB @-@ 10 was eventually joined in the Flanders Flotilla by UB @-@ 2 , UB @-@ 4 , UB @-@ 5 , UB @-@ 6 , UB @-@ 12 , UB @-@ 13 , UB @-@ 16 , and UB @-@ 17 ; of these , only UB @-@ 2 made the journey to Flanders by sea rather than rail . 
The first Type UB I to enter service was UB @-@ 10 , which formed the nucleus of the Flanders Flotilla , on 27 March 1915 . By the end of April five more Type UB I boats done become operational . UB @-@ 10 was eventually joined in the Flanders Flotilla by UB @-@ 2 , UB @-@ 4 , UB @-@ 5 , UB @-@ 6 , UB @-@ 12 , UB @-@ 13 , UB @-@ 16 , and UB @-@ 17 ; of dese , only UB @-@ 2 made the journey to Flanders by sea rather den rail .