To enable tanks in the battle mode you must get a medal in all of the stages in the main game. (NOTE: To get the medals each stage must be acomplished with a certain number of kills, also you must keep all of your wingmen alive).
To fight on foot in battle mode with bazookas you must (after getting all the medals on the regular mode) get every medal on expert mode. (NOTE: Medals are achived the same way as before).