>characterized as Russian and 'highly concerning''
https://www.popularmechanics.com/military/navy-ships/a42537023/russia-poseidon-torpedo/
Powered by a compact nuclear reactor, it is believed the Poseidon could travel at unprecedented speeds of 100 knots (185 kilometers per hour), have a range of approximately 10,000 kilometers, and operate at depths of up to 1,000 meters. Designed to evade detection by acoustic tracking devices and other traps, the Poseidon has a diameter of approximately 1.6 to two meters. Particularly riveting is the torpedo’s devastating payload: a nuclear warhead with a likely yield of at least several megatons (with early reports suggesting it could yield up to 100 megatons).
https://thebulletin.org/2023/06/one-nuclear-armed-poseidon-torpedo-could-decimate-a-coastal-city-russia-wants-30-of-them/