Sadly, dolphins are another common target for conscription. They are smart mammals. The ones in Sevastopol could be considered turncoats, having transitioned through Soviet->Ukrainian->Russian hands. They're basically swimming guard dogs.

There is a joke about intelligent apes like orangutans and chimpanzees: they could probably learn to speak, but they refuse to do so out of fear that people would try to employ them.

Well I remember a US movie of the 1970's with George, C. Scott:

https://en.wikipedia.org/wiki/The_Day_of_the_Dolphin

though admittedly in the fiction the dolphins were trained to place the explosives and leave.

About the supposed use of dolphins in Sevastopol:

https://www.livescience.com/russians-using-military-dolphins...

they seem like a marine version of the good ol' Roman geese:

https://en.wikipedia.org/wiki/Brennus_(leader_of_the_Senones...

a sort of intrusion alarm.

citation?