This achievement is for completing the first 3 of 9 stronghold missions.
To unlock these missions so that they show on the map, you'll need to meet each faction leader and start doing quests for them to increase their influence on the island. To start a mission, make your way to the icon on your map and you'll be transported to the mission start with a short explanation of the mission objectives.
All missions essentially require you to storm a government base whilst escorting a technician/hacker to an area where he can access the base defences. If the you or the hacker dies, you'll need to start the mission again.
- Take your time but bear in mind the hacker and his team will slowly move forward and leave you behind if you're too slow. Try and keep youself between the enemy and the hacker at all times.
- The other team faction members you start with are useful but dispensible - only worry about keeping the hacker alive.
- If you see a gun turret, detach it and use it for as much of the mission as possible - the ammo will never run out. Bear in mind carrying this will slow you down, so try extra hard to keep up with your team.
- As you move through the base, take out any SAM sites you see. If you find a military helicopter, by all means use it, but beware of further SAMs you may not have found yet - these should be your first target and once they're out of the way, you should be able to dominate from the air.
- Try not to get distracted by destroying other targets while you move through the base - only base defences should be removed, everything else can be mopped up after the stronghold is yours.
- The end of the mission will always be a standoff while you wait for the hacker to do his thingand this usually ends with the base commander appearing in a tank or a helicopter. Usually there is a gun turret at these locations, so man it to take out the enemy troops and destory the commander's vehicle.
- Remember you can use your zip line to pull enemies from high walkways and roofs. There are usually many enemies in high places during these missions.