Transwarp drive was a term applied to some types of propulsion technologies that overcame the limitations of conventional Warp Drives.
Technology
Federation Transwarp Drive
The Great Experiment
The USS Excelsior was employed by Starfleet to test the Federation's version of the transwarp drive in the 2280s. By the following decade, however, the ship used a standard warp drive. Dilithium used in all Federation warp cores becomes unstable at the high warp frequency essential in the Federation transwarp design. Achieving warp 10 was never possible on the Excelsior.
Flight of the Cochrane
In 2372, a new form of dilithium was discovered from an asteroid field in the Delta Quadrant by the crew of the USS Voyager, which stayed stable at high frequencies. In transwarp simulations at speeds exceeding warp 9.7, tritanium depolarization created a velocity differential between the nacelles and fuselage of the ship. Lt. Tom Paris of the Voyager managed to adapt the quantum warp theory and the multispectral subspace engine design by setting up a depolarization matrix around the fuselage of the craft. In this design, the craft was first taken past warp 8 with traditional warp drive, and then switched over to transwarp drive for the warp 10 acceleration.
The Class 2 shuttle Cochrane was taken on the first manned flight through the warp 10 threshold into subspace. Piloted by Paris, he described the time he spent in infinite velocity as for a moment being everywhere. The crew of the Voyager hoped to return home earlier than expected, but navigation inside infinite velocity was something that remained untested. The first test flight returned the Cochrane into the exact same spot in space where it had crossed the barrier.
Unfortunately for Paris, the effects of crossing the transwarp threshold on a Human soon became apparent, as Paris went into cellular mutation. His DNA began to rewrite itself within a day through what appeared to be possible future Human evolutionary stages over the coming millions of years. Even killing Paris with high levels of radiation, while trying to stop the transformations, failed to stop the mutation that quickly revived him to life again. Finally becoming mentally unstable, Paris kidnapped Captain Kathryn Janeway and took her on another transwarp journey; this time, he was able to navigate the ship and emerge near a jungle planet. By the time the Voyager found them, they had both mutated into amphibian-type creatures and reproduced. The offspring were left in their new environment.
Highly focused antiproton radiation was used in controlled five-second bursts to deteriorate all mutated DNA in the bodies; thus forcing all mutated cells to revert to the original DNA coding that was still present in small traces in the amphibian bodies of Paris and Janeway. Their original genomes stabilized three days after treatment.
A Speedy Gun
As experimental Starship, USS Bathala (NX-95670-A) was developed by Section 31 with a Transwarp Drive fully operational and without the side effects caused by the previous uses of a drive of this kind. But the Warp Drive wasn't removed, both being there, and the Transwarp Drive only working for when it's necessary more speed.
Epoch Transwarp Drive
Built for Speed both inside and outside Warp Speed, and for time travel, the Epoch Mark 3 has its own version of the Transwarp Drive, using technology from another universe, in this case, the universe from where Ciel came.
References
- Memory Alpha, Transwarp Drive