In 2375, during the Dominion War, he was assigned to AR-558, a planet that the Federation Alliance had captured from the Dominion. His commanding officers were Captain Loomis and Commander Parker. Fellow members of his unit included Reese, Vargas and Nadia Larkin.
Eight months later, the majority of the original members assigned to protect the planet's communication array were dead, including Loomis and Parker. Larkin now commanded the troops. Kellin was killed in the final Jem'Hadar attack against AR-558 before the arrival of reinforcements and relief from the USS Veracruz. (DS9: "The Siege of AR-558")