Multiplayer: Fire Controller
Use each offensive support action once (awarded at end of round)
On the lower right of your screen, you will see a number like 0/50 above your ammo count. This is your scorechain. You build scorechains by getting Kills (10 pts), Kill Assists/Savior Kills/Revenge Kills/Headsohts/Melee (5 pts), Completing Objectives (15-50+ pts) and using Defensive Support Actions (30-100+ pts). Once you've fulfilled the quota, a support action will be made available to you. Press to use an Offensive Support Action, is for Defensive Support Action. Keep scoring more points to increase your scorechain to a higher level and gain more powerful support actions. If you die, your scorechain resets, but if you obtained a support action before you died and didn't use it, it will still be available when you respawn.
You DON'T have to use all of them in one session, it can be done over multiple sessions.
If you want to gain the higher level support action quick, use Defensive Support Actions on the lower levels because they give you guaranteed points that count towards increasing your scorechain to the next level. This is a list of all available Offensive Support Actions, thanks to eldraco:
Level 1 - Mortar Strike (50 Points)
Level 2 - Rocket Attack (100 Points)
Level 3 - Missile Attack (175 Points)
Level 4 - Artillery Strike (250 Points)
Level 5 - Strafing Run (350 Points)
Level 6 - Air Strike (450 Points)
Level 7 - Cruise Missile (600 Points)