The test verified propulsion technology developed through more than 180 tests over the past five years, KCNA said, adding that AI was used for target detection and guidance in the new high-speed precision-guided torpedo.
The test is the latest in a run of North Korean weapons launches. It comes amid heightened tensions on the Korean Peninsula, as both Koreas race to develop weapons capable of evading missile defences.
The test was part of routine defence research activities aimed at advancing the country's weapons systems, KCNA said, adding that it demonstrated improvements in propulsion efficiency and the performance of the torpedo's rocket propulsion system.
The latest test came after North Korea said it had tested two types of submarine-launched strategic cruise missiles on Wednesday to verify its navy's mission capabilities and the reliability of its war deterrent.
Pyongyang has been seeking to develop modern missile submarines alongside ballistic and cruise missiles, test-launching them from various platforms, including an ageing submarine.
Meanwhile, South Korean President Lee Jae Myung oversaw the country's first test-firing of a domestically developed hypersonic missile last week.
Seoul's test of a hypersonic glide vehicle, a manoeuvrable weapon that can change course during flight, came days after North Korea said its leader, Kim Jong-un, had also overseen a test of an intermediate-range hypersonic missile.
