Tactical Tip: The only truly safe places in Terra are inside forts or in deep water. If you are going to be away from your keyboard, evac or swim first.
Once you have built your Castle or Mobile Base you must set defenses to protect your fort from enemy attack. There are a number of structures that you can place around your fort that will help defend your hard-earned assets from marauding opponents.
Use @power to place, then @build to complete.
Power Plants are used as a source of energy to power your Clan's Castles. They are not required at a Mobile Base (which is self-powered) Without a Power Plant a Castle cannot power its defenses or FARP any vehicles. When built within 500m of its owning Castle a Power Plant (PP) will act as a permanent Repulsor Field between itself and the Castle... not allowing any enemy land vehicles to pass between the two structures. Power Plants take up one defense slot at a Castle.
Use @radar to place, then @build to complete.
These structures can be built as part of the defenses at any Castle or Mobile Base. A Radar station allows a Clan to detect any completed enemy Castles or Mobile Bases built within a 20km radius. Incomplete structures will NOT be detected. Any structures found by your Clan's radar stations will automatically show up on your Clan's Satellite Map. If a new building is completed and is within the detection range of one of your Clan's Radar stations while you are online, you will be notified by a warning message on your Radio Message Console. Building Radar stations fill one defense slot at a Castle or MB.
Use @th to place, then @build to complete.
Thugs are heavily armed and armored gun emplacements that can be built around your Castles and Mobile Bases. They are stationary defenses and will fire on any enemy vehicles that they detect in their vicinity (detection range will vary depending on whether they and/or their targets have their IFF systems engaged).
Players can enter Thugs to assist in the defense of their bases (simply "lase" the Thug by right-clicking your mouse then use the @e Radio Command to go inside). Thugs are armed with a Main Gun (using both DUP and HEAT rounds) as well as HSM and LDM missile racks and a Machine Gun. Thugs require one defense slot to build.
Use @rep to place, then @build to complete.
A Repulsor Pole, or "Rep" is a Force Field generator used to prevent enemies from being able to get close enough to your fort's Communication Pylons to shoot them with their Machine Guns. An invisible electromagnetic field is created between any two Repulsors (or between a Repulsor and your fort or Power Plant) as long as they are within 500m of each other. Any vehicle attempting to drive between the Reps will be "bounced" back 200m by the force field. Each Repulsor required one defense slot to build.
Use @decoy to place, then @build to complete.
A Decoy Pylon like those found at the Beachhead Plus Castles can be constructed at your Outland forts. They look just like a regular Communication Pylon but will explode when fired upon within 100m. Decoys require one defense slot to build.
Use @ammo to place, then @build to complete.
An Ammo Dump (AD) can be built anywhere on the Terra map as long as it is at least 1.5km from any other structure. Unlike most other structures Ammo Dumps can be used by any players in the game regardless of their Clan affiliation. Parking next to an Ammo Dump and pressing your SUP key (or 0 on your NumberPad) will allow you to repair any damage to your vehicle and reload any expended ammunition. Ammo Dumps do not count against the defense slots at your fort.
Use @fuel to place, then @build to complete.
Just like Ammo Dumps a Fuel Dump can be constructed anywhere in the Outlands or Beachhead areas as long as it is at least 1.5km from any other structure. When you SUP a Fuel Dump you will refill your vehicle's fuel tanks. These structures can be used by any player regardless of which Clan they were built. Fuel Dumps do not count against fort defense slots.
Use @crate to request a resupply drop.
Supply crates can be summoned from nearby forts in order to replenish your ammunition without building an Ammo Dump or finding a wreck to SUP. It will be delivered by Bloodbat aircraft to your location and dropped nearby. It will show up BLUE on your Satellite Map. Crates do not count against the defense slots at your fort.