EA-3148 (Substance 100A)  is a "V-series" nerve agent related to the better-known compounds VX and VR. It was studied by both the US and Soviet chemical weapons programmes during the Cold War, and is notable as the only V-series organophosphate nerve agent specifically identified in public domain sources as having a higher absolute potency as an acetylcholinesterase inhibitor than VX (around 50% more potent by weight). However, both the US and Soviet investigations of the compound concluded that despite its high potency, the physicochemical properties of the substance made it unsuitable for weaponisation, and further research was not conducted.
The chemical structure of EA-3148 falls within the scope of compounds designated "Toxic chemicals" under Schedule 1 of the Chemical Weapons Convention and so it is illegal throughout the world under international law and may only be used for certain types of scientific and medical research.