This is a thoroughly enjoyable read, and one I’d recommend.
Alastair Mars had a somewhat checkered career, which adds interest to the story of a man who served to his utmost capacity, and was in effect punished for it later.
Regards, Uyraell.
Looks good, I just put it in my Amazon cart. Thanks for the recommendation.
You are more than welcome. 
Alastair Mars did write a follow-up book, though I’ve long since lost memory of the title.
I don’t think he wrote more than 4 all told though, and I’ve long since lost memory of the titles of all except “Unbroken”.
It would not take much to search out what Mars did write, however, most were originally published between about 1956 and 1962.
My first ever copy of “Unbroken” was the 2nd imprint, 1956. My current copy is from the 7th imprint, 1960.
If you’ve an interest in submarine operations, I’d also take the trouble to search out Waldron and Gleeson.
These two fine authors published two books well worth searching for.
“Above us, the waves” covers the British “Chariot” manned torpedo raid against the Tirpitz, and the later X-craft raid.
“The divers” expands a little on the theme of the first, and covers the training and operations of some of the RN volunteer divers in X-craft and XE-craft.
Kind and Respectful Regards, Uyraell.
Good, another addition to my collection!