 Germany and Bulgaria negotiated the purchase of two <unk> I boats for the Bulgarian Navy , <unk> @-@ 7 and <unk> @-@ 8 , in 1916 . Two crews of Bulgarian sailors were sent to Kiel for training . Before the purchase could be completed , <unk> @-@ 7 was sunk , leaving only one boat for Bulgaria . On 25 May 1916 , <unk> @-@ 8 was officially transferred to Bulgaria for the remainder of the war . 
