Mixed-Tech and Terrain
In the original Armada II game, by capturing a construction ship of a different faction you would get the ability to build the whole technology tree of this other faction. Since it would be quite implausible to see a Klingon warrior of the Empire captaining a Dominion V-13 Battleship, in Fleet Operations this feature has been removed.
Instead, in Fleet Operations there are certain ship classes that can only be acquired by building a mixed tech yard. There are two methods to gain access to a mixed technology facility. If you have an ally that is of a different faction, you can build a mixed tech facility with your own construction ship immediately. The second method available to build a mixed tech structure is to capture a construction ship (which needs to be of a different faction) and build a mixed technology facility with it. Each faction has its own mixed tech station. After building this special facility, you must research Analyze Alien Technology before you can build any mixed technology starships. If you have multiple allies (or multiple captured alien construction ships), you only need to Analyze Alien Technology once to gain access to all of the units from each shipyard. Note that the Borg need only build their Adaption Matrix to gain access to mixed-technology benefits. Once this is built, the Adaptor chassis can be outfitted with Adaption Modules.
Mixed tech vessels can be completely new classes or simply improved designs that you have already seen in your other shipyards. Usually the improved designs are more expensive than the regular ones and are slower to build. Each brand new class of mixed technology unit (the Romulan Saeihr, Federation Miranda II, and Klingon E’Djen) consumes one mixed-tech slot out of a maximum of 20, except for the Dominion V-15 Dreadnought, which consumes 10 slots out of a possible 20 (each mixed tech yard does not count separately towards this limit). Thus, for instance, you may build two V-15 Dreadnoughts (any type or combination, but only two total) and an unlimited amount of mixed technology T-15s.
Notice that while Dominion, Federation, Romulan, and Klingon mixed-technology facilities do not have repair bays, the Borg Adaption Matrix grants you the ability to repair any assimilated vessels.
There are 5 different types of nebulae in Fleet Operations. The types of nebulae are: Crystalid (a green nebula that disables cloak and regenerates shields), Fluid (a blue nebula that disables cloak and shields), Tetrion (a blue nebula with lightening that disables cloak and causes damage), Nucleon (a sickly red nebula that disables cloak and causes damage), Mutara (a purple nebula that disables shields, sensors and cloak, and hides vessels inside). Tetrion deals twice as much damage per second as the Nucleon nebula.
Note that there can be different types of nebulae all in the same place. The effects of those nebulae are the combination of every nebula's effects.