The "USS Dauntless" was an alien starship disguised as a Federation Dauntless-class starship that was in service to Starfleet in the late 24th century. Allegedly, the Dauntless was the prototype for its class of starship.
In mid-2374, while still stranded in the Delta Quadrant, the USS Voyager received a transmission from Starfleet Command via the ancient Hirogen communications network. Although the message contained a number of unencoded personal messages, there was also an encrypted file that the Voyager crew was unable to open.
On Stardate 51978, Voyager encountered an alien named Arturis who had a gift for translating languages, both verbal and visual. He easily decrypted the mysterious message, which gave a set of coordinates near their current location. Upon arrival, the Voyager crew discovered the Dauntless, which activated its quantum slipstream drive when the away team of Chakotay, Tom Paris and Tuvok boarded it to travel fifteen light-years in a few minutes.
Although intrigued at the drive's possibilities and its promise of a faster trip home, the Dauntless was relatively minimalist by other Starfleet standards, possessing only one transporter and no replicators, holodecks or shuttlecraft. While investigating the Dauntless, it soon proved to be an elaborate trap set by Arturis to arrange for the Voyager crew's assimilation by the Borg, with its resemblance to Starfleet technology the result of Particle synthesis, an advanced form of replicator technology. Arturis's race had been recently assimilated by the Borg, and Arturis blamed that event on Kathryn Janeway's short-lived alliance with the Borg against Species 8472.
He had assumed that the crew's desire to get home would prompt them to immediately take the ship and use the slipstream to try and get back to Earth, only learning after activating it that it was programmed to take them to Borg space, but past experience and an unwillingness to abandon Voyager prompted the crew to carry out various tests first. After Janeway decoded enough of the original message to reveal that Dauntless was a trap, Arturis attempted to simply take Janeway and Seven back to Borg space, but Voyager was able to duplicate the slipstream and rescue them, leaving Arturis stranded aboard the Dauntless as it entered Borg space, where he was presumably assimilated. (VOY: "Hope and Fear")