An EV pack was equipment that Starfleet officers wore on training missions.

At one point during the Omega training mission on Titan in 2147, the EV pack that Commander Charles Tucker III was carrying froze up, causing him to develop nitrogen narcosis. In his narcosis induced delerium, Tucker attempted to remove his helmet. However, Archer was able to convince the commander to remain calm and keep his EV pack intact. (ENT: "Strange New World")