Chinese engineers recently published an article in the Journal of Field Robotics, in which they talked about the testing of a new hybrid aircraft called Nezha-SeaDart with a fixed wing and the function of vertical take-off and landing (VTOL).
Nezha-SeaDart capable of vertical take-off and landing both from the ground and from – under water, to smoothly cross the boundary of the “water” boundary air» and move under the water column like an autonomous underwater vehicle.
Military submarines can be equipped with a similar device in theory.