There are 2 repositories under ardusub topic.
Howto use BeagleBone Blue with ArduPilot
ArduSub: An ROV control system, now an official part of the ArduPilot project!
Companion computer startup scripts and examples
Tools to run ArduSub localization experiments
A set of ROS package for the BlueROV and ArduSub compatible vehicles.
Aquadrone project to position a sub with 50cm accuracy into water. It is working with BlueROV2 from @Bluerobotics and a Reach RTK from @emlid. It is a French project.
A BlueOS Extension that listens for NMEA messages (GGA and HDT) and sends position information to the Water Linked UGPS system