The Omega training mission was an exercise on Titan involving Jonathan Archer and Charles Tucker III in 2147. At one point during the mission, Commander Tucker's EV pack froze up causing him to develop nitrogen narcosis. In his narcosis-induced delirium, Tucker attempted to remove his helmet. Only Archer was able to convince him to remain calm and keep his EV pack intact.
In 2151, while under the influence of tropolisine on the planet later known as Archer IV, Archer recalled this incident in an attempt to persuade Tucker into taking an injection of inaprovaline. Ultimately, Tucker's hallucinations proved to be too overwhelming a force for the Omega reference to be of any use. (ENT: "Strange New World")