The vessel was powered by three ion motors and did not have time travel capability, nor was it armed. It was designed (according to the Gallifrey Databank) to be an extension of K9's own computer systems. Its top speed was unrevealed. It was described as white, triangular and smooth.
There were in fact two K-NELs. The first was destroyed while battling the renegade Time Lord Omegon, after which the Time Lords gave K9 a replacement vessel, K-NEL Mark II, which was identical to the original bar the addition of red stripes along the sides. (PROSE: K9 and the Time Trap)
The level of interconnection between the vessel and its pilot was extreme. The controls for the craft were directly linked into K9's central computer, allowing him to operate it merely by thinking. This instantaneous communication between pilot and craft allowed for a manoeuvreability that "often save[d] K9 from destruction".