Privateer

This requires the TEC Primacy's unique planet item for building pirate ships; the "Pirate Mercenary Base".

Once you have this, build enough ships to use up 500 supply. The supply cost for each ship is displayed below the icon image for each ship type. The Pirate Corsair has the highest supply cost at 16 points, so you'd need to build 32 of these ships.

See also Armada for more about fleet supply.