The extension was first devised by the Doctor after he had added daydreaming subroutines to his program in 2376. His initial request to Captain Janeway for the subroutine to be added to his program was denied, but after the Doctor demonstrated his abilities in practice, Janeway reconsidered and ordered a research in the Doctor's command abilities. (VOY: "Tinker, Tenor, Doctor, Spy")
In 2377, Janeway added the command subroutines to the Doctor when tetryon radiation forced everyone to abandon ship. After the ship was abandoned, before the Doctor could begin repairs, Voyager was attacked. He and the computer disabled one ship and evaded others to hide in a nebula. He managed to begin repairs, yet life support wasn't online by the time Chakotay, Harry Kim and Neelix returned after an away mission.(VGR: "Workforce, Part I").
After Chakotay and Neelix went to find the rest of the crew, Harry and the Doctor disagreed about who was superior to the other. In one battle with the Quarren, the Doctor called up information about a Romulan battle from his tactical database, leading to him using a photonic shockwave against the ships, before retreating. In the final battle against the Quarren, it was Harry's plan to sabotage three escape pods and detonate them once in the enemies' tractor beams that saved Voyager. The Doctor learned a lesson about experience, and that he was needed as a medic more on Voyager than a commander, and made peace with Harry before handing back command to a recovered Captain Janeway. (VGR: "Workforce, Part II").
In 2378, the Doctor, disguised as Chakotay, used Chakotay's codes to transform himself into the ECH. As the ECH, the Doctor had the authorisation to eject the warp core, which he did. He then escaped the ship aboard the Delta Flyer with the warp core, to exchange for Captain Janeway's freedom from the Overlookers. (VGR: "Renaissance Man").
- It is unclear of the future of the ECH concept following the Voyager's return to the Alpha Quadrant. There is an obvious potential to Starfleet for this technology, but it is unlikely that many Captains would relish the concept!