MISSION 12 - An Act Of Piracy
Mission Area: Cauda
After talking to the mercenaries during the scenes, you'll end up in control of Rico next to a light plane. Hop in the cockpit and fly out of the cave and into the open sky. You'll be traveling a good couple of kilometers so taking the plane is the fastest way there. Fly over the marker in the town of Ponere and jump out, parachuting down to the location of the tank (which is sitting in the middle of a road flanked by two trucks).
The main ability of this tank (besides launching damaging shells at targets) is that it can generate a glowing blue shield that prevents all incoming damage and bounces you off if you attempt to grapple onto it when active. However, it can only do this periodically, not all the time. So you need to carefully time your grapple after the shield ends and quickly hijack (Y/ Triangle) the tank as soon as you land on top before the next shield activation.
If you're quick, you can get inside the tank before it starts moving up the road (moving makes it slightly harder to aim your grapple). When you successfully take over the tank, a new arrow path will appear ahead of you for you to follow. You can also use the tank's shield ability by pressing in the left stick to protect yourself from damage. Use this when incoming attacks are about to hit for maximum effect. The tank has plenty of health and the shield prevents large chunks of damage as long as you activate it so simply trundle along the marked path, blasting your way through a couple of vehicle blockades until you reach the dock at the end and carefully drive it onto the boat. Pretty easy overall.