In 2372, unit 3947 (who had, at that point, been in service roughly 150 years) was badly damaged and adrift in space after its asteroid mining pod was disabled. It was later discovered by B'Elanna Torres, who, with the assistance of The Doctor, Harry Kim, and Kathryn Janeway, was able to repair it.
The unit was polite and gracious to Lt. Torres and full of praise for her skills and abilities. Torres found it to be sentient, and it communicated with her in a male voice. The unit then beamed Torres aboard one of its sister ships. He wanted Torres to build a module that could be used to build more models like himself.
At first Torres helped the units by building a prototype, on the threat Voyager and her crewmates would be destroyed. As the pair worked, they conversed about his creators and exchanging information about her own culture; 3947 was particularly fascinated to learn about Data, a machine like himself but nevertheless treated as an equal to the Builders. However another ship with similar units appeared and fired on the Pralor starship, revealing the truth about the conflict between the two sides. Torres destroyed the prototype before being beamed aboard one of USS Voyager's shuttlecrafts piloted by Tom Paris. (VOY: "Prototype")