While serving on the planet Serenno, CT-3278 and two other clone stormtroopers were sent to the location of a crashed cargo container that had been hijacked by the rogue clones of Clone Force 99. Using BARC speeders, the three stormtroopers arrived at the container's location and set up a small perimeter. While searching the crash site, they eventually spotted Echo inside the container and opened fire, but the latter managed to close the container's door, trapping himself and rogue clone Omega inside.
In the meantime, CT-3278 reported his findings and requested backup while one of his comrades set up a mounted cannon. After a while, another rogue clone of Clone Force 99, Tech, arrived and stunned one of the stormtroopers. CT-3278 and the other remaining stormtrooper proceeded to pin down Tech behind a tree with heavy blaster fire. CT-3278 ordered his subordinate to hold fire as he approached the tree, but was quickly disarmed by Tech. Engaging in hand-to-hand combat, CT-3278 threw Tech to the ground and attempted to wrestle away control of the commando's DC-17 hand blaster, but was ultimately overwhelmed by Tech. After shooting down the gunship that CT-3278 had called in, Clone Force 99 would thereafter escape in their ship the Marauder.
As a clone of bounty hunter Jango Fett, CT-3278 stood 1.83 meters tall, had black hair, brown eyes, and tan skin.
As a clone stormtrooper, CT-3278 wore standard-issue Phase II clone trooper armor that was devoid of any color or markings.