He served as relief helmsman during Travis Mayweather's absence when an away team explored an uninhabited planet (ENT: "Strange New World") and when the crew made contact with the Novans. (ENT: "Terra Nova")
He manned the helm again when the ship was under the command of Lieutenant Malcolm Reed (ENT: "The Andorian Incident") and when Enterprise made a secret first contact with the Akaali/ Malurians. (ENT: "Civilization")
Tanner served as relief helmsman during the absence of Travis Mayweather when Enterprise had to deal with an unidentified species. In the current time he served in the aft section on the bridge and reached Captain Archer a flashlight when the main power went offline. (ENT: "Silent Enemy")
He was also on duty on the aft bridge when the ship made first contact with the Valakians, and visited later the mess hall later, (ENT: "Dear Doctor") and when a group of Vulcans came aboard. (ENT: "Fusion")
In early 2152, Lieutenant Reed was hoping to add a third officer assigned full time to the armory, this would give Tanner the time to begin upgrades to the torpedo launchers. Tanner was later wounded when a mine exploded on the hull of Enterprise and was brought into sickbay by Crewman Rossi. (ENT: "Minefield")
Tanner recovered and served at the helm when communications officer Hoshi Sato tried to talk to the Kreetassans (ENT: "A Night in Sickbay") and when Malcolm Reed and Captain Archer had to search a lost communicator. (ENT: "The Communicator")
When the crew was forced to live and work at the catwalk for a few days, he manned the temporary helm control at the catwalk when Captain Archer requested him to relieve Travis Mayweather from the makeshift after he passed the ship through a maze of plasma eddies. Later he participated in watching another film for the movie night. (ENT: "The Catwalk")
Tanner was working on the bridge when Commander Tucker and the Arkonian Zho'Kaan went missing on a desert planet (ENT: "Dawn") and when Captain Archer and Ambassador Soval tried to implement peace talks with an Andorian group led by Commander Thy'lek Shran on the planet Weytahn. (ENT: "Cease Fire")
Tanner was working in the engine room when the three Orion women D'Nesh, Maras, and Navaar came aboard. Like every male aboard the ship he was also affected by the Orion pheromones and witnessed a dispute between Commander Tucker and Kelby. Later, when Harrad-Sar tried to hijack Enterprise and Captain Archer, Tanner was working on the bridge. (ENT: "Bound")
Tanner was identified by name in "Minefield" and "The Catwalk." In his final appearance he wore no rank insignia, implying the rank of Crewman. This was likely a costuming mistake, but it is equally likely that the character was also demoted.
He was also featured in the extended deleted scene in sickbay in the episode "Minefield". A distressed uniform worn by English in his performance as Tanner was sold off on the It's A Wrap! sale and auction on eBay. 
(This list is currently incomplete.)
- "Broken Bow"
- "Strange New World"
- "Terra Nova"
- "The Andorian Incident"
- "Fortunate Son"
- "Silent Enemy"
- "Dear Doctor"
- "Vox Sola"
- "A Night in Sickbay"
- "The Communicator"
- "The Catwalk"
- "Cease Fire"
- "The Breach"
- "The Xindi"
- "Storm Front"
- "Storm Front, Part II"
- "Observer Effect"
- "The Aenar"
- "These Are the Voyages..."