[epoxy_sauce]

Dolphins maybe

https://en.m.wikipedia.org/wiki/Military_marine_mammal

[escapecharacter]

I'm aware of the dolphins. It's become an in-joke among friends that the Crimean invasion started to get the military dolphins back for the cable attacks.

However, dolphins don't have as much depth capacity as other whales. I'd choose sperm whales for this, if they were trainable: https://en.wikipedia.org/wiki/Physiology_of_underwater_divin...