This page contains significant spoilers from ArmA 3's 'The East Wind' and 'Apex Protocol' campaigns.
The Eastwind device is a CSAT weapon of mass destruction (WMD) that is believed to be capable of causing earthquakes.
Its exact date of origin is not known, though due to the brief tremors experienced during the events of the Prologue, it is possible that it was already halfway or close to completion more than year prior to The East Wind.
In the Apex Protocol campaign, Captain Miller reveals that he believes the device was used to cause the tsunami that wreaked havoc across Tanoa. Throughout the campaign, NATO intelligence suggests that the device produces foreshocks as part of its arming sequence.
At the end of the Apex Protocol campaign, Miller secures the Eastwind device and airlifts it to an undisclosed location.
How the device exactly operates is not elaborated on in either of the campaigns. However, it is clear that the process has a significant startup delay since the device must be manually armed.
It also must be physically deployed on-site to have any effect and can't be used to trigger earthquakes remotely. But once armed, brief tectonic shockwaves are always a prelude to the actual earthquake.
|«|| We don't know - MEDCOM's got no idea what's causing it - according to seismic monitoring, this is abnormal activity.|
One notable fact about Eastwind is that it is capable of causing earthquakes in regions of the Earth which do not naturally experience any seismic activity on a regular basis. Examples include both Altis and Tanoa, with the latter also triggering a tsunami in the aftermath of the initial quake.
Though it's never revealed publicly, Eastwind's military and geopolitical uses are shown to great effect throughout both campaigns in ArmA 3.
It forms the cornerstone of CSAT's so-called 'Apex Protocol' plans that seek to destabilise countries that have favourable relations to the West. By triggering Eastwind in a specific country, the natural disasters caused by it are used as a pretext for CSAT to provide humanitarian aid and relief (on top of chaos caused by Viper operatives covertly operating in the country). This then leads to the establishment of CSAT military bases in that country in exchange for continued support.
Because Eastwind's effects are practically impossible to trace back to their source, it can be used without fear of retaliation as opposed to the likes of nuclear WMDs.