Well I have to say I am not impressed with this series, and I know I am in the minority. So let me explain why is that.
When it comes to writing in my opinion it is nicely done. Actually very good compared to many ww2 fiction books, even though there were at times to much "tell don't show " for my taste.
Our main mc is very well written character. I really like him, his character development and his journey through the books. I have no complaints there. But the praise mostly ends, other parts of these books are at best "meh" to me.
Secondary characters for example. They are really underdeveloped and mostly cookie cutter. The main reason for this in my opinion is that we change the setting and set of characters way to much through these books. Because of this I failed to have any real attachment to any of them, from friends and subordinates, to love interests.
Now the romance subplots. They were really badly done, mostly the romance with Shirley. It was underdeveloped, not explored enough, and went from zero to a hundred in no time! Author had 6 books to do it organically and build it up, but I think he put the romance as a mandatory thing in naval war fiction, and didn't give it much thought afterwards. I won't waste words on Malta episode.
Then the "Bonny boy" the villain. He is the worst part of this series. Waaaay to evil, that he seemed like he came out of some Disney cartoon. No character development for him. Just like romance with with Shirley, he seems to put in the books to fill mandatory "evil superior officer who hates the main mc". And that is fine, I actually like that trope. But then you have to develop that said character, his motivations, aspirations or insanity. Not just plop him in the story.
So in the end I gave it three stars instead of two. After all I have read and paid for 6 books. In the end i believe it is good enough to read, but I doubt it deserves all these glowing 5 star reviews it gets on kindle and goodreads. There are much better books and series of this type out there, that should not be put in the same category with this one.