CT-27-3555 was a clone of the bounty hunter Jango Fett who was born on the planet Kamino to serve in the Grand Army of the Republic. Early during the Clone Wars between the Galactic Republic and the Confederacy of Independent Systems, CT-27-3555 was part of Bravo Squad, a squad of clone cadets training on Kamino. During their training, Bravo Squad was able to successfully complete the practice test in record time. When ARC trooper Commander Colt of the Rancor Battalion arrived to oversee the final exams, Bravo Squad, along with Domino Squad and two other units, were summoned to a hangar in Tipoca City Military Complex for Colt's speech and his introduction by Master Chief Bric. During his speech, Colt selected Bravo Squad for the final test first due to their record time in completing the practice test.
Starting Citadel Challenge version THX variable 1138, CT-66-3232 and CT-66-3233 took the left flank while CT-66-3238, CT-66-3339, and CT-27-3555 took the right flank. CT-66-3232 directed CT-66-3238 and CT-66-3339 to move forward and engage the training battle droids while they followed close behind and the others provided cover fire. The squad moved up, reaching the base of the citadel and eventually CT-66-3339 told CT-66-3238 to move forward to the citadel. CT-66-3238 was able to rappel up and capture the light post, completing the exam. While exiting the arena, CT-66-3555 and their teammates passed the incoming Domino Squad, while CT-66-3233 mocked them.
During training, CT-27-3555 demonstrated that they had teamwork skills and effectively coordinated with the rest of Bravo Squad.
CT-27-3555 was equipped with clone training armor which contained the red coloring of Bravo Squad, the number five on their chest plate and left shoulder armor, had their designation on their left leg, and utilized a DC-15A blaster carbine with non-lethal bolts and an ascension cable.
This Bravo Squad cadet's identification number was first depicted in the episode "Clone Cadets" of Star Wars: The Clone Wars. It says 27-3555, and the prefix CT- was predetermined. This way of determining identification numbers was proved with the troopers in Domino Squad.