Love HRO. Read many times.

4 other books I love about Subs. 2,3,4 a bit pulpy and clearly written on the coat-tails of HRO but I enjoyed them for the time they were written in. And Patrick Robinson is excellent.

Another Patrick Robinson Submarine book is HMS Unseen, been quite a while since I read it tho, it kind of follows on from Nimitz Class and Kilo Class and leading to Seawolf featuring some of the same characters.

Also Sea Leopard by Craig Thomas of Firefox fame, it is about the hunt for an elusive submarine and trying to capture it, it is book 3 in a series of spy thrillers, as a kid I used to play around some of the areas where some of the action happens and it captures the areas quite well.