Is the Poseidon Real? The Diplomat's Doomsday Weapon vs Russia's Actual Torpedo

That announcement came 13 days after Season 3 of The Diplomat premiered on 16 October 2025.

Putin gave no location or other details, AP reported, and Euronews noted that there was no independent confirmation that the test took place. Putin also claimed that the power of the Poseidon's nuclear warhead is "significantly higher than that of our most advanced Sarmat intercontinental ballistic missile." Russian media have gone further, reporting speeds of up to 200 km/h and a design to explode near coastlines and unleash a radioactive tsunami, according to AP.

What experts say about the Poseidon

Russian tsunami claims have targeted Britain before. In 2022, Russian state TV presenter Dmitry Kiselyov said a Poseidon explosion near the British coast would cause a tsunami up to 500 metres high, and all three experts Euronews consulted judged that unrealistic. "It could wipe out a coastal city but not the UK as a whole," Sidharth Kaushal told the outlet.

On the weapon itself, in May 2025 the FAS judged it "unlikely that the Poseidon is already operational." It also recorded an apparent aborted test in November 2022 and a throw test of a mock-up from the Belgorod in January 2023.

Georgia Cole of Chatham House told ABC News: "There's no independent verification of the tests or the actual performance of these weapons." The Bulletin noted in 2023 that many see it mainly as a "psychological weapon".

How The Diplomat compares with reality

The biggest difference is certainty. In the show, the Poseidon is supposed to be a rumour until the lost submarine turns out to be carrying one, and the United States then takes it. In Season 4, Callum Ellis (Aidan Turner), who works in British intelligence, suspects the weapon has been taken, having spotted that radiation levels around the submarine have changed. In reality, The Insider reported in August 2026 that "there is no confirmation that it exists as a finished, deployable weapon."

Netflix's recap is also more definite about what the weapon does, describing the show's Poseidon as "a salted bomb designed to maximize radio fallout". That echoes the leaked 2015 document. But the FAS describes the real weapon's large warhead as rumoured, and The War Zone calls the accuracy of the dirty-warhead and tsunami reports debatable.

Some details line up closely. The show's submarine shares its name with the actual Sarov, which the Bulletin says is believed to have been modified to test Poseidon prototypes. Kate's cement plan follows a real structure too: Runit Dome on Enewetak Atoll, which the US Department of Energy says was completed in 1979 and holds over 100,000 cubic yards of radioactively contaminated soil and debris.

Why the Poseidon matters to the story

Much of Season 4 grows out of the theft. In Episode 1, Callum's suspicion forces a lie: on Grace's orders, Kate gives him a false explanation. In Episode 3, a budget discrepancy in the plan to bury the submarine in concrete threatens to expose the cover story, and Hal tells Trowbridge the truth.

Trowbridge's successor, Bethan Vaughn (Jodie Whittaker), then agrees to let Russia retrieve the bodies of its dead crew, which would let the Russians discover that their weapon has been stolen. Grace orders Kate to warn Vaughn off with the threat of US warships, and Kate never delivers it. By the finale the warships are deployed, and at the G7 summit Grace admits the US took the Poseidon and then threatens to open fire on interfering countries, allies included.

Cahn spelled out the stakes when discussing Season 3. "That would make a lot of people really angry: both Russia, who made the weapon, and the UK," she told Tudum of the seizure. "Hal and Grace are playing with matches in somebody else's house."