This structure is the light guard tower, which is available from the start without research. It can be build quickly and supports any weapon type (if connected to the conveyor network if needed for the weapon) , but due to its cheap design this tower cannot hold against larger attacks. Usually a few shots can bring it down (even fewer from heavy weapons) but it's cheap and fast to build. Weapons on towers have a higher visual range and can have a first shot at enemies before they come into range of their own weapons.
In order to support walls (see the other image) and a conveyor connection that needs to cross the walls, the guard tower (like it's heavy armored larger brother) have diagonal conveyor connections.
(Blender render without nodes or postprocessing)
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