For this, you need to earn all 5 Rebel skills.
You can see which skills you do and don't have by holding the right bumper down.
In case you don't know what the icons look like on the map, they are:
• Vehicle Drop Off - Car with an arrow behind it
• Diversion - A man holding a gun with an arrow behind him
• Mortar Support - Mortar shell with an arrow next to it
• Spotting - Eye, triangle with an arrow next to it
• Guns for Hire - Pistol with an arrow next to it
You can more than likely get this through natural progression, but for the group that enjoys knocking things out quickly, this can help.