Upon acceptance of "UB-8" by the Bulgarian Navy, she was renamed "Podvodnik No. 18" (in Cyrillic: "Подводник №18"). Although the commissioning ceremony for "Podvodnik No. 18" was kept out of newspapers, it was attended by Crown Prince Boris and his brother Prince Kiril, who both boarded the submarine for a ceremonial first voyage to Euxinograd, the Bulgarian summer palace located just north of Varna. In Bulgarian service, the submarine was armed with a deck gun that supplemented its machine gun.