Either start a new campaign or resume an existing one from the main menu. 
Return to the main menu select any single mission. Enter the briefing area and 
select armament. Choose a very large herc and return to the briefing area. 
Cancel the single mission. Resume the campaign from the main menu, play through 
the first assigned mission and then save your game. Load your saved game back 
up and all hercs will be available to you fully loaded.