Faster-than-light, also called superluminal or FTL, communications and travel refered to the propagation of information or matter faster than the speed of light.
In the Post Diaspora era, humans had found means to travel faster than light with the discovery of hyperspace and the invention of the impeller drive, the Hyper generator, and the Warshawski sail. (HH1)
Faster-than-light communication by anything but courier was something humanity kept looking for for a thousand years, but remained impossible until Manticore's breakthrough at the beginning of the 20th Century PD. (HH14) By using a specialized gravity generator to create rapid pulses that could be detected by gravity sensors (which can detect gravity waves in real time), the Royal Manticoran Navy was able to communicate in realtime across the full range of their gravity sensors (to all practical purposes, anything short of interstellar range). (HH9, HH10)
This capability was used not only in ships but also in recon drones and twenty years later was compact enough that it was theoretically possible to fit it into an MDM at the expense of one of the impeller drives (although the RMN took a different route developing Apollo).
The spread of this technology was extremely slow. The defection of Erewhon from the Manticoran Alliance gave the Republic of Haven their first look at functional units almost two decades after their initial deployment. The Solarian League had no known samples and although they were familiar with the theory by 1921 PD, did not appear to have solved the engineering problems as of the Second Battle of Manticore.
The Andermani Empire developed and deployed FTL equipped recon drones around 1918 PD. The first confirmed use was by the IANS Hellbarde while shadowing the HMS Jessica Epps in the Harston System. (HH10)
The Republic of Haven deployed FTL communications equipment before the early 1920s PD. The first known use of FTL technology by Haven was during the Battle of Solon with the Tarantula platforms. (HH11)
Hermes Buoys were communications platforms, equipped with FTL grav-pulse receivers and transmitters, light-speed communication lasers and other standard sub-light communication capabilities. They were designed to be long-range communication relays with a transmission speed of about 64c. (SI2, HH11)
- Admiral Sonja Hemphill began developing the idea following a report on a tactic Captain Honor Harrington used in Silesia to signal to IANS Neue Bayern. HMS Fearless flickered her wedge causing a gravitational pulse, which effectively moved faster than light and was visible to Warshawski detectors. (HHA4.2: WOS)
- Detailed article on the faster-than-light concept on Wikipedia