The Defiant pathfinder was a Federation Starfleet starship design from the 2360s. It was proposed as a fast torpedo attack ship to penetrate threat defenses at high warp, but never got off the drawingboard.
An existing spacecraft design, NXP-2365WP/T, which had just entered the initial systems-level review stage, was chosen as the basis of the Defiant pathfinder proposal. It would have been a dedicated warship capable of firing photon and quantum torpedoes at speeds of up to warp 9.982.
It also spawned a specialized four-nacelled, twin-cored high-warp courier ship capable of covering over 50 light-years within six days, equivalent to warp 9.92. This modified vessel successfully surpassed the 1,000 light-year/year efficiency barrier. (DS9 reference: Star Trek: Deep Space Nine Technical Manual)