Xindi ships emerge from a subspace vortex.
Degra's shuttle inside a subspace vortex
A subspace vortex (also called an energy portal) was an extremely fast method of propulsion utilized by the Xindi. Capable of transporting a vessel dozens of light years in a matter of hours, the vortices were opened through the generation of a phase deflector pulse. (ENT: "The Shipment", "Stratagem")
A subspace vortex was used to transport the Xindi superweapon to Earth, escorted by Commander Dolim's ship, in 2254. While Enterprise remained in the Delphic Expanse in an attempt to disable the Sphere network, Captain Archer boarded Degra's ship in pursuit, accompanied by Lieutenant Reed and a team of MACOs. Degra's ship, which was significantly faster, was eventually able to close the gap and arrive at Earth shortly after the weapon, but not in time to stop Dolim from destroying the Yosemite 3 research outpost. (ENT: "Countdown", "Zero Hour")