The Silent Enemy aliens, which STO have called Elachi, are to be allies of the Tal Shiar, here's the in-universe story of their return, from STO's announcement:
Although reports of similar alien encounters have been recorded as far back as the 22nd Century, it wasn't until their ships first appeared in Romulan space that the Elachi finally came to be known by name. Since these mysterious, silent adversaries began working in concert with Tal Shiar forces, they have mounted a series of devastating attacks on colonies and settlements and are believed to be responsible for hundreds – possibly even thousands – of disappearances in this region of known space. These abductions have struck fear into the hearts of many species in the Alpha and Beta Quadrants, and people across the galaxy now look into the skies and wonder if the Elachi will be coming for them next.As usual, these new releases to STO come in the form of opportunities to pick up a selection of themed items from a lock box, and Lobi crystal exchange. There are two Elachi ships available, the S’golth class escort, which is reminiscent of the original Enterprise design:
During the many clashes between Elachi and the Romulan Republic and its allies, many examples of Elachi technology have been recovered and are being adapted to help fight these silent enemies. Elachi technology may even allow ships to someday explore subspace, where the Elachi apparently have the ability to safely travel and even construct stations for their fleets.
Study of this technology is still ongoing, but initial findings indicate a possible link between the Elachi and artifacts of Iconian origin. What the connection between these species could be is yet to be determined. And the Elachi themselves have not been known to talk about anything, much less divulge the secrets of their origins.
And the Monbosh class battleship, which also have the ability to launch fighters:
Also included in this release is an Elachi bridge design, new weapons, such as the distinctive crescent weapon, Elachi ground-combat robotic drones, and the usual assortment of mirror universe versions of other STO ship designs. See a few examples of those, and a look at STO's Voth, after the jump@
For more on the Elachi, see STO's announcement, and ship stats article. Coming to the game in a future update are the Voth, the Delta Quadrant descendent of Earth's dinosaurs featured in Voyager's Distant Origin. There story will apparently tie into a Dyson Sphere. STO has released lots of concept art featuring both subjects. Here are a few examples:
Incidentally both the Elachi and the Voth have been featured in Star Trek books by Christopher L. Bennett. His version of Silent Enemy aliens, known informally as the Mutes, and more correctly as the Vertians, are the antagonists (or so it appears at first) in his new Enterprise novel Rise of the Federation: A Choice of Futures. The Voth meanwhile had a major role to play in in his alternate universe Voyager story Places of Exile, which can be found in the Myriad Universes anthology Infinity's Prism.