No Naval Police? Really?
I am like dramas like this and it has a top notch cast. However, I did wonder about its accuracy. Would the Royal Navy allow a civilian police officer on board a nuclear submarine? The Navy does have its own police force, just as the Army has one. Think NCIS.
The reason that Amy Silva is sent is explained away early on. The boat was still in Scottish waters when the death took place. This seems like a dramatic liberty designed to create conflict between the Navy and the Police.