This does have a military application. Submarines can deploy these UAVs near enemy coastlines where they can do then launch from underwater when ordered to do some aerial recon. They can transmit what they see back to control centre then when mission ends, can go back underwater again and wait for the next signal... "Researchers at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, have developed an innovative unmanned aerial vehicle (UAV) that can stay on station beneath the water, then launch into the air to perform a variety of missions.

The Corrosion Resistant Aerial Covert Unmanned Nautical System — or CRACUNS — is a submersible UAV that can be launched from a fixed position underwater, or from an unmanned underwater vehicle (UUV). A team from APL’s Force Projection Sector worked with fabrication experts in the Research and Exploratory Development Department to create a new type of unmanned vehicle that can operate effectively in two very different arenas: air and water."