The Siege of Dac, also known as the Battle of Mon Calamari, Capture of the 4th Fleet and Destruction of the Dac Shipyards was a decisive battle during the Sith Crusade.
Following the Battle of Ossus the Sith Fleet jumped to Dac and procceded to surround the planet, effectively besieging it.
Fortunately for the Sith the Alliance relief fleet that had arrived an Ossus was on course for Dac and as such the planet was lightly defended.
Several Sith boarding forces were also dispatched to capture much of the fleet that had been under Darth Abeonis' control during his rather brief first fall to the dark side.
They succeeded and then went about destroying the orbital shipyards with the very vessels they had just captured.