During the early stages of the Clone Wars, CT-66-3339, a clone cadet, served as a member of Bravo Squad, which was a training unit. On their clone training armor, they bore the marking of the number four.
On the planet Kamino, CT-66-3339 was born as a clone of Jango Fett, the bounty hunter. CT-66-3339, like their fellow clones, was created to fight for the Grand Army of the Republic. During the initial period of the Clone Wars fought between the Galactic Republic and the Confederacy of Independent Systems, CT-66-3339 was assigned to Bravo Squad, a squad of clone cadets undergoing training on Kamino. Squad Bravo distinguished themselves during training by setting a new record for the practice exam. Commander Colt, an ARC trooper from Rancor Battalion, arrived to oversee the final evaluations. Bravo Squad, alongside Domino Squad and two additional units, were summoned to a hangar located within the Tipoca City Military Complex to hear Colt's address. Because of their speed in the practice test, Colt chose Bravo Squad to be the first to take the final test.
In Citadel Challenge version THX variable 1138, CT-66-3339, along with CT-66-3238 and CT-27-3555, were assigned to the right flank, while CT-66-3232 and CT-66-3233 took the left. CT-66-3232 instructed CT-66-3238 and CT-66-3339 to advance and engage the training battle droids, while they provided support from behind along with the rest of the squad. The squad advanced and eventually reached the citadel's base. CT-66-3339 then instructed CT-66-3238 to move towards the citadel while the rest of the squad provided covering fire. CT-66-3238 successfully scaled the citadel and secured the light post, with CT-66-3339 following closely, thus completing the exam. As they were leaving the arena, CT-66-3339 and their squadmates passed Domino Squad, and CT-66-3233 taunted them.
CT-66-3339's gear included clone training armor adorned with the red markings of Bravo Squad, the number four displayed on their chest plate and left shoulder armor, their designation inscribed on their left leg, and a DC-15A blaster carbine that fired non-lethal bolts, along with an ascension cable.
The identification number of this Bravo Squad cadet was first seen in the Star Wars: The Clone Wars episode "Clone Cadets". The number shown was 66-3339, and the CT- prefix was predetermined. This method of assigning identification numbers was confirmed with the troopers of Domino Squad.