I'd like to achieve 4.5 foot depth underwater. I thought a BT module or WIFI board would work fine sealed in a submarine. Radio communication reflects off water? Also, what if I heat shrink-wrap an ultrasonic ping sensor, mount it on top the hull and use it for obstacle avoidance? Will the chirp and echo work underwater?
Natures warning sign: If any of that worked, you would see a lot of projects already using it.