Chernobyl has become the third best ever launch for an original drama on Sky Atlantic with its opening episode scoring a cumulative audience of 1.7M.

The HBO co-pro, which is produced by Jane Featherstone’s Sister Pictures, was the biggest audience for a Sky original drama this year and its launch is only behind Fortitude, which was Sky’s entry into premium drama in 2015, and Amazon epic fantasy co-pro Britannia.

This figure includes linear ratings, catch-up screenings and video-on-demand data across its first seven days. The second episode of the show has already hit 1.5M viewers but has yet to fully consolidate.

Chernobyl tells the story of the 1986 nuclear accident in the Soviet Union and stars Jared Harris, Stellan Skarsgård and Emily Watson. It dramatizes the true story of one of the worst man-made catastrophes in history and tells of the brave men and women who sacrificed to save Europe from unimaginable disaster. The miniseries focuses on the heartbreaking scope of the nuclear accident that occurred in Ukraine in April 1986, revealing how and why it happened and telling the shocking, remarkable stories of the heroes who fought and fell.

Harris plays Valery Legasov, the Soviet scientist chosen by the Kremlin to investigate the accident; Skarsgård plays Boris Shcherbina; the deputy chairman of the Council of Ministers and head of the USSR’s Bureau for Fuel and Energy; and Watson plays Ulana Khomyuk, a Soviet nuclear physicist committed to solving the scientific mystery of what led to the disaster at Chernobyl, so that it can be prevented from ever happening again.

The five-part series was written by The Huntsman: Winter’s War’s Craig Mazin and Featherstone recently told Deadline that Mazin’s initial outline was “one of the most fascinating, compelling and brilliant outlines I had ever read”.