 Germany and Bulgaria negotiated the purchase of two UB I boats for the Bulgarian Navy , UB @-@ 7 and UB @-@ 8 , in 1916 . Two crews of Bulgarian sailors were sent to Kiel for training . Before the purchase could be completed , UB @-@ 7 was sunk , leaving only one boat for Bulgaria . On 25 May 1916 , UB @-@ 8 was officially transferred to Bulgaria for the remainder of the war . 
 Germany and Bulgaria negotiated the purchase of two UB I <a href='uninflect' title='1'><mark>boats</mark></a> for the Bulgarian Navy , UB @-@ 7 and UB @-@ 8 , in 1916 . Two crews of Bulgarian sailors <a href='uninflect' title='2'><mark>were</mark></a> sent to Kiel for training . Before the purchase could be completed , UB @-@ 7 was sunk , leaving only one boat for Bulgaria . On 25 May 1916 , UB @-@ 8 was officially transferred to Bulgaria for the remainder of the war . 
Germany and Bulgaria negotiated the purchase of two UB I boat for the Bulgarian Navy , UB @-@ 7 and UB @-@ 8 , in 1916 . Two crews of Bulgarian sailors was sent to Kiel fir training . Before da purchase could b completed , UB @-@ 7 was sunk , leavin only one boat for Bulgaria . On 25 May 1916 , UB @-@ 8 was officially transferred to Bulgaria for tdaremainder of the war .