How do you engage a Beloved?

By trial and error I’ve figured out that those manta like things in the unterzee are the Beloved. To all tests they seem completely docile and my weapons won’t target them. Yet you’re supposed to be able to send them to the Gant Pole and I imagine they’re used in other stories?

Is this a bug, or is there something I need to unlock?

Just click on one and your weapons should target it.