Convoy missions are radio tag missions meaning they are triggered randomly. These kind of missions first available when the player libarated the Parker sector. There are two variants of the convoy missions:
In the "destroy" variant, as it's name suggests, the player is tasked to destroy an EDF Convoy. The targets are usually fuel transport trucks. The best way is to destroy the convoys to set up an ambush then take out all the trucks at once.
In the "hijack" variant the player is tasked to hijack either an EDF APC or a fuel transport truck. The transport truck is usually harder, since it lacks of armor and speed. Once the vehicle is captured the player has to drive it to the marked safe house.
In both missions the reward is morale boost, or ,in the case of Convoy: Destroy, some salvage from the destroyed vehicles.