Gammack, a Mon Calamari Captain, was a member of the Third Battalion. He fought in the Battle of Calamari during the era of the Galactic Civil War.
During the conflict, Captain Gammack gave the order for evacuation shuttles to move to the forward positions, with the purpose of extracting the injured before the World Devastators could overwhelm their defenses. He voiced his disagreement with the order to retreat to a more distant location, but was informed this was to avoid being caught in a wedge formation created by the Devastators.
Following a short discussion, he received authorization to transmit a communication to the Republic base located on the moon of Da Soocha V. His message was only partially completed, because the World Devastators arrived at his location before he could finish sending it.
When Lando Calrissian's strike force arrived at Dac, Green Leader reached out to Gammack, instructing him to ready his forces for extraction. Gammack conveyed his gratitude and communicated to the squadron leader that his battalion was the only remaining unit in that sector of the battle. Upon the Devastators deploying the TIE/D automated starfighters, he alerted Green Leader to the fighters pursuing him, but was unable to prevent Green Leader's demise.
As the battle turned against the New Republic's favor, he made an attempt to reinforce his soldiers' remaining Amphibion assault boats in preparation for a boarding action against the nearest Devastators. When the ships were affected by the overriding command signal, Gammack's troops boarded the Devastators and fought their way onto their decks. They were then instructed by the crew of the Millennium Falcon to abandon the vessels as they were about to be destroyed.