In May 1916, the submarine was transferred to the Bulgarian Navy as Podvodnik No. 18 and commissioned in a ceremony that was attended by Crown Prince Boris and Prince Kiril.
U svibnju 1916. godine podmornica je prebačena u Bugarsku ratnu mornaricu kao Podvodnik No. 18 i stavljena u službu u ceremoniji kojoj je nazočio krunski princ Boris i princ Kiril.