Balok's pilot vesseledit this page

From Memory Alpha, the free Star Trek reference

The pilot vessel used by Balok was a small ship capable of enormous power. It controlled the flagship Fesarius and was equipped with a tractor beam. Besides Balok, no crew was needed.

On Stardate 1514.1, the USS Enterprise was forcefully towed by it and could only free itself under great risks. (TOS: "The Corbomite Maneuver")