First assignment after Academy: Engineer's mate, U.S.S. Exeter, 2262. Promoted to lieutenant, junior grade, in 2263.
In 2264, transferred to U.S.S. Lexington as a junior engineer, 2264. Earned navigator certification and promoted to lieutenant, 2265.
Transferred to U.S.S. Enterprise (NCC-1`701) in 2266 as relief navigator. Nearly destroyed the Enterprise in 2266 when he fell under the effects of the Psi 200 virus and shut down the ship's engines, causing the vessel's orbit to decay rapidly.
In late 2266, witnessed the death of Anton Karidian, a.k.a. Kodos The Executioner, aboard U.S.S. Enterprise during a performance of "Hamlet." (During childhood on Tarsus IV, had been one of nine surviving eyewitnesses to KodosΓÇÖ slaughter, along with future Starfleet captain James T. Kirk. RileyΓÇÖs parents had perished.)