The Gantries are structures common to the UEF and the Cybran Nation. They construct land and aerial experimentals, much like Land and Air factories. They are available as soon at least one experimental are researched.
Both land and air gantries are required to build the respective experimental units by UEF and Cybran ACUs. The Illuminate only need to build one; The Experimental Gantry to construct both types but requires more space to build.
Naval Experimentals are built traditionally in the water and do not require a Gantry.
Since each Experimental Gantry can construct all Experimental Illuminate units you have unlocked, your opponents won't know if you will be attacking from Land or Air until construction begins. With proper scouting, though, a canny opponent can learn exactly what is being built, as the unit is clearly visible during the entire construction process.
On maps like Geothermal Borehole where base space is at a premium, the Illuminate Experimental Gantry is superior because you otherwise simply may not have room for both an Air Gantry and Land Gantry.
All experimental units can be launched "Half-Baked", causing them to enter play at half health and with some miscellaneous problems as well (indicated by a small lightning bolt on their model) This problem can NOT be fixed, so its not recommended to use this ability for mass production
It is not recommended to send out half-baked models without fixing them, as the malfunction condition they suffer from reduces their effectiveness greatly, and is irrepairable.