Anti-Aircraft Site Tau is an FND flak post in Aguas Lindas, Madrugada. It protects FDA Airbase Olimpia, so it stands between you and safe flying around that airbase. Destroying it also gets you Depleted Uranium.
The site is built around a large framed anti-aircraft gun, a scaled-up version of a twin-barrel ZU-23 cannon, with two shoulder-fired missile launchers mounted beside it. FND soldiers guard the position, and the Depleted Uranium is kept somewhere on site for you to grab. It protects FDA Airbase Olimpia, so it stands between you and safe flying around that airbase.
Do not fly in. The site warns you over the radio, then opens fire, so arrive by road, boat or on foot. Scout from higher ground first and tag the guards with your phone. Like other FND positions, watch for alarms and cameras and shoot them before you go loud. When you reach the gun, one rocket or a Supremo blast is normally enough, or toss two or three grenades onto it.
You get the Depleted Uranium stored at the site, which is the main way to fund Supremos and Resolver weapons outside the Du or Die story mission. The airspace over this part of Madrugada also opens up, so you can fly here and use Air Drop.
After the story, Insurgencies let the FND Remnants retake anti-aircraft sites. You can destroy this one again when that happens, but you can never hand it back to the FND yourself.
Anti-Aircraft Site Phi
Anti-Aircraft Site Phi is an FND flak post in Aguas Lindas, Madrugada. Its name is easy to mix up with Pi and Psi, so check the letter on the map before you head out. Destroying it also gets you Depleted Uranium.
Esperanza West Checkpoint
Esperanza West Checkpoint is an FND roadblock in Aguas Lindas, Madrugada. Clear it for XP, a key to its locked room and a local contact who marks nearby anti-aircraft sites, ambushes and FND bases on your map.
Ída's Refuge Checkpoint
Ída's Refuge Checkpoint is an FND roadblock in Aguas Lindas, Madrugada. Clear it for XP, a key to its locked room and a local contact who marks nearby anti-aircraft sites, ambushes and FND bases on your map.
Anti-Aircraft Site Eta
Anti-Aircraft Site Eta is an FND flak post in Costa del Mar, Madrugada. You find it up on Pino Crest, which gives the guns a wide view of the coast below. Destroying it also gets you Depleted Uranium.