While undergoing her first sea trials, "Delfin"s ballast tanks were faulty and it took 12 minutes to complete her dive. This foreshadowed future events for the vessel. On 29 June 1904 the submarine sank in the Neva River by the wall of the Baltic shipyard during a test dive. The captain and 24 crewmen were killed, and 12 men were rescued. The vessel was raised 3 July and transferred to the Siberian flotilla, arriving in Vladivostok in late 1904. "Delfin" returned to service in February 1905.