If your mothership is low-observable/submersible you could park it in a harbor and when time is right unleash a swarm of hybrid aerial underwater drones with mission payload.

This design uses 1 swashplate server plus 1 brushless drive motor for each prop for a total of 8 motors. Designs in Ukraine are now using 1 brushless drive motor to synchronously drive all 4 props and 1 swashplate servo each prop, reducing total number of motors to 5, which might be a natural path of optimization for this type of hybrid aerial underwater?