I decided to watch this series largely because I've enjoyed Suranne Jones’s performances across numerous projects since her early work on Coronation Street. It speaks well of her both as an actress and someone who consistently picks interesting stories. The connection between her character and DS Longacre, which is revealed mainly through flashback sequences, occasionally feels predictable, but it didn't bother me too much. I found the way they incorporate it—using a kind of coded memory system to allow Longacre to communicate with Suranne’s character while avoiding detection—to be clever. I did see that on one particular online platform, despite the show earning what seemed like a well-deserved high rating, there were numerous very negative reviews. Some of those criticisms centered around the diversity of the cast. While most people seem happy to move past decades of limited representation by white, straight men—a group I happen to belong to—there’s still a small number who can't accept it, even if they attempt to justify their opinions in brief comments. There were also some complaints that the numerous and severe technical failures experienced by the submarine would be unrealistic. However, this is make-believe, and I don’t mind them opting for dramatic plot twists rather than a more gradual narrative progression. One viewer even pointed out inaccuracies regarding military protocols. But my enjoyment of a show isn't dependent on whether or not they get those kinds of details right. Regardless, it was enjoyable—which is ultimately what I want from something intended to be entertaining.

Source on TMDB