each team can declare one assault, designating a player to lead the strike force and targeting a specific location on the map. Then, the other team must choose a player to defend against the assault
This makes me think that the attacking team decides the flight they will attack with (from one of their 3 already built fleets) and who will be the player to attack, The defenders then choose which fleet is defending and which fleet defends.
I can only guess it will be the same as normal Armada and you will not know the makeup of the fleet beyond it's one of the 3 fleets in the campaign.
Then again, maybe you can build more than 400/500 worth of fleets and choose which ships you deploy?