From Rusty and Jacob of ArduSub:
Hello everyone, Rusty here at Blue Robotics. We're pleased to announce that the ArduSub project has merged with Ardupilot!This is a momentous occasion for the ArduSub project, with our two main developers, Jacob and Rusty, both becoming members of the ArduPilot development team. ArduSub is the first new vehicle type since the addition of ArduBoat in 2011, and is the first to take the ArduPilot project underwater! We've been looking forward to seeing this since the start of ArduSub!