This new troop transport warning

I started a new game with the new patch, and occasionally get the "warning, troop transport approaching" warning when I'm shooting up a base .....

I've never seen one though - I hang around deliberately waiting, but nothing.

Has anyone seen one?
Are they real?
If you have seen one, what do they actually do??? Fly near you and shoot you, or drop drones off??

I'm hoping this is not a gimmick to get you scared and run away from the base you're attacking ....