The mission is to intercept a military convoy travelling through the Grand Senora Desert and steal the cargo in the barracks. This is a setup mission for the Paleto Score heist. Once you have hijacked the truck drive it either as Michael, Trevor or Franklin, back to the meth lab. You then make a call to Lester to tell him you have done the job to end the mission.
Intercept the military hardware
Go to the heist setup icon on your map and approach the military convoy to begin this mission.
Approach the convoy head on, eliminate the soldiers and steal the truck containing the hardware, taking care not to damage or destroy the truck itself.
Tip! Start this mission as Trevor, as you'll be able to make use of his special ability to help you eliminate the soldiers.