The primary warp coil of an Illyrian starship
A primary warp coil was an integral component of warp-powered starships. It was a type of warp coil.
In 2154, the Enterprise NX-01's primary warp coil was damaged beyond repair due to a Xindi attack. In order to make a rendevous with Degra on time, Captain Archer was forced to mount an attack on an innocent Illyrian starship for the purpose of stealing their warp coil. (ENT: "Damage")