IP cameras that do not require Internet?

I want to install some IP cameras on tugboats. While these boats have Wi-Fi on board, they do not always have a connection to the greater Internet. (They have LTE hotspots that work near the coasts.) I would like crew to be able to view the cameras from various points on the boat at all times and for land staff to be able to view the cameras when the boats have an Internet connection.

It looks like the Ubiquity applications used to support these modes but the newer "Unifi Protect" lines expects to use cloud services.

I realize I can cobble together something that works in both modes. I am wondering if anyone has experience with hardware/ecosystems that do not assume the cloud is omnipresent.

Edit: I guess I should have made this clearer. I want the users to be able to use the same UI/app whether local or remote, assuming it will do NAT traversal in the remote case.