Commandos should have a hijack command to hijack ships:
Country A has a Battleship lv.4, while Country B only has a level 2, B wants a level 4, so he/she sends commandos to hijack A's Ship, if the hijacking is successful, B now has a level 4 Battleship and unlocks that unit on there research tree, even though only level 2 was researched.
If the commandos fail, they all are either killed or questioned and troops of Country B are revealed.
As I said before, hijacking would unlock that level of the ship, unless its an elite unit and you don't have the blueprints, its already a researched level, your corresponding unit was never researched, or its a nuclear unit.
Country A has a Battleship lv.4, while Country B only has a level 2, B wants a level 4, so he/she sends commandos to hijack A's Ship, if the hijacking is successful, B now has a level 4 Battleship and unlocks that unit on there research tree, even though only level 2 was researched.
If the commandos fail, they all are either killed or questioned and troops of Country B are revealed.
As I said before, hijacking would unlock that level of the ship, unless its an elite unit and you don't have the blueprints, its already a researched level, your corresponding unit was never researched, or its a nuclear unit.