One of my favorites!
All 3 books in the first uplift series work fine as stand-alone stories. But book 1 (Sundiver) does kinda read like a prequel to the rest of the series. The inciting incident of Startide Rising is what sets everything else in motion for all subsequent books, and Sundiver takes place before that. But it does have a bunch of world building that is helpful context for the other books (and is still a fun story).
I recommend you read Startide Rising first, then circle back to Sundiver if you are enjoying the world and the author's style.
They don't need more training. They need consequences