Is The Diplomat Based on a True Story? The Real History Behind the Show

A real HMS Courageous was sunk in 1939 by the submarine U-29. Royal Museums Greenwich records that it went down on 17 September 1939, while on anti-submarine patrol off Ireland, "with the loss of 518 of her crew, including her captain."

Scotland, Faslane and the Creegan base

Grace's motive draws on real Scottish politics. Netflix's Tudum says she "conceived the strategy as a way to halt the momentum of Scotland's secession movement". The fear was losing Creegan, a fictional Scottish nuclear submarine base that Tudum calls "the only base in Europe where Americans can dock their nuclear submarines."

Tudum says Creegan is based on His Majesty's Naval Base, Clyde, more commonly known as Faslane. The Royal Navy says the base, "commonly known throughout the Navy as Faslane", is home to the core of the Submarine Service, including "the nation's nuclear deterrent". The SNP says: "In an independent Scotland, the SNP would seek to negotiate with the rest of the UK for the removal of Trident from Faslane."

"When I was growing up in Scotland, we actively talked about Faslane," executive producer Janice Williams told Tudum.

Is the Poseidon in The Diplomat real?

Yes, in the sense that Russia runs a real weapons programme called Poseidon, though the show's story around it is invented. In Season 3 a Russian submarine carrying the Poseidon torpedo goes missing off England's northeast coast. Grace, now president, and her vice president, Hal Wyler (Rufus Sewell), secretly send an American submarine to capture it. Tudum describes the lost vessel as a nuclear-powered B-90 Sarov submarine, and Russia has a real submarine called Sarov, which the Bulletin of the Atomic Scientists says is believed to have been adapted for testing Poseidon prototypes.

On 1 March 2018, during his state-of-the-nation address, Vladimir Putin presented the actual Poseidon, an underwater drone, AP reported. On 29 October 2025, 13 days after Season 3 premiered, he said it had been tested the day before, according to AP. Federation of American Scientists researchers, writing in the Bulletin of the Atomic Scientists, judged in May 2025 that it is "unlikely that the Poseidon is already operational."

The plan Kate pitches to encase the submarine in concrete also has a real model: the Runit Dome in the Marshall Islands, which she cites on screen. The US Department of Energy describes it as "a containment structure on Runit Island, located on Enewetak Atoll", completed in 1979 and holding over 100,000 cubic yards of soil and debris that are radioactively contaminated.

Real politics behind Season 4

In the closing moments of the Season 4 premiere, Grace is shot outside Windsor Castle by a sniper. In Episode 2, Grace transfers presidential power to Hal before her surgery, and he temporarily takes on presidential duties. Off screen, the process for a handover like this is Section 3 of the 25th Amendment, ratified in 1967: a president's written declaration to the President pro tempore of the Senate and the Speaker of the House that he cannot carry out his duties passes them to the vice president "as Acting President". George W. Bush used it in 2002 and 2007, and Joe Biden in 2021, per the Congressional Research Service.

In the finale, Stuart objects to Grace's decision to send warships into British territory in a cable sent through the State Department's official dissent channel. Even though Secretary of State Miguel Ganon (Miguel Sandoval) shares the cable's view, Grace orders Stuart recalled to Washington. The Dissent Channel itself was created by Secretary of State William Rogers in 1971, per the State Department, and the Foreign Affairs Manual states: "Freedom from reprisal for Dissent Channel users is strictly enforced." In our reading, that rule is what makes Grace's response so stark.

In the same episode, with US warships already deployed, the new British prime minister, Bethan Vaughn (Jodie Whittaker), calls an emergency session to invoke NATO Article 4. The article says members "will consult together" when any of them believes "the territorial integrity, political independence or security of any of the Parties is threatened", which can lead to joint action but does not require it. NATO's page, last updated in September 2025, counts nine invocations since 1949, including two in September 2025: by Poland over Russian drones, and by Estonia over Russian jets in its airspace. The difference on screen is that the warships heading for British waters are American.