“William Shirer wrote [the 1941 bestseller] ‘Berlin Diary’ and literally all my research was in that book, which told what it was like to be  in Berlin in the three years leading up to the war,” says Hunt, 56. “That book landed in my lap thanks to [series] writer Peter Bowker. Shirer was hearing all the propaganda and being called to press conferences to hear Hitler paint his situation as though he was the one being victimized.

“Claire Hollingworth … was a relatively new reporter living and working on the Berlin-Polish border,” she says. “She went out to get coffee one day and saw German tanks hidden behind burlap sacks that were hanging on a fence. She went home and called her paper and said, ‘It’s happening tomorrow’ and they said to her, ‘You better be sure — we’re putting it on the front page.’

“I remember reading that she called her paper the next day and held the phone out the window [so they could hear the gunfire and chaos] and said, ‘It’s happening right now!’”

In “World on Fire” — premiering April 5 on PBS and Masterpiece — the American journalist Campbell, who’s based in Berlin, works for the American Radio International network, filing daily dispatches to her listeners back home while trying to dodge the German censors parsing her every word. She’s alarmed by what she’s seeing, and warns her closeted gay nephew, Webster O’Connor (Brian J. Smith) — a doctor working in a Paris hospital — to return to the States as soon as he can (he doesn’t listen). As German troops storm into the Polish territory of Danzig, we meet the series’ other main characters, all tied to the conflict in different ways and in different countries. There’s Harry Chase (Jonah Hauer-King), an interpreter at the British embassy in Berlin who’s in love with both Lois (Julie Brown), a Manchester nightclub singer/rebel, and Polish waitress Kasia (Zofia Wichlacz), whose family takes him in; Harry’s elitist, cold-as-ice mother Robina (Leslie Manville) and Lois’ working-class dad, Douglas (Sean Bean), a pacifist trying to keep his family together; and Gregor (Mateusz Więcławek), Kasia’s younger brother who joins the Polish resistance and experiences the brutalities of war.

The 10-episode series, which premiered on  BBC One last September and was renewed for a second season, was filmed mostly in Prague. “It was one of the few European cities not decimated in the war,” Hunt says. “When I was there, I got a lot of conflicting reports from the Czech people, like, did they fight [the Nazis] hard enough? Could they have fought harder? In all of these cities, the pain is still so deep.”

Hunt, who reteamed with “Mad About You” co-star Paul Reiser for a revival of their popular ’90s-era NBC sitcom — it aired on Spectrum last November and December — says there’s no word, yet, on a Season 2.

“Not that I know of,” she says. “I know that through the lens of Spectrum they seemed to be very happy with how we did [the revival]. We were very adamant that we didn’t want to commit to more than one season because we didn’t know how this would go.

“I’m very proud of it,” she says. “We didn’t blow it. That’s how I feel. If it had been a lame reboot we all would’ve felt really bad — and I feel like we got out of there alive.”