 In September 1915 , UB @-@ 7 and UB @-@ 8 were sent to Varna , Bulgaria , and from there , to patrol off the Russian Black Sea coast . On 18 September , UB @-@ 7 torpedoed and sank the British steamer Patagonia about 10 @.@ 5 nautical miles ( 19 @.@ 4 km ; 12 @.@ 1 mi ) from Odessa . The cargo ship , of 6 @,@ 011 gross register tons ( GRT ) , was the only ship credited to UB @-@ 7 , and the only one sunk by any of the Constantinople Flotilla in the month . 
