The Bilbringi asteroid fields that surrounded the Bilbringi Shipyards made the shipyards there almost unassailable. The only way to mount an attack was to jump to hyperspace and then revert to realspace inside the perimeter. During the early days of the Rebellion, this maneuver was tried. The Millennium Falcon piloted by Quip Fargil was meant to impact with the shipyards, the Falcon was carrying a Baradium fission device. Using the Falcons exceptional hyperdrive he could jump bypass the asteroid fields. The mission was a failure because Fargil couldn't bear to destroy the Falcon, he jumped to Vaced before reaching the shipyards.