The Nebula-A was a type of warship equipped with ion cannons. One of them served as Osten Dal'Nay's flagship during his time as commander of the Cularin Militia. It acted in a customs capacity, regulating traffic in the Cularin system after the system withdrew from the Galactic Republic. It would ionize and pull aside any ship that acted irregularly.
Appearances
The Price of Neutrality -- Isolation on Wizards.com (backup link) (original site is defunct)