The Empire had largely ignored the swampy world of Taul and were unaware of the existence of a small Rebel base there. The Empire discovered the Rebel presence by chance. One of the probe droids sent out by the empire to find the Rebel base on Hoth was dispatched to Taul. When the Empire lost contact with the droid, they sent the Victory-class Star Destroyer, the Dominator to investigate the matter.
The dominator arrived out of hyperspace in the morning local time, and immediately began dispatching troops to the surface of the planet. Due to the conditions of the battlefield, the empire did not use heavy walkers, but deployed battle skiffs, attack droids, swamptroopers, and repulsorlift-equipped spacetroopers instead. The repulsorlift-based battle platforms and troops made it easier for the Imperials to traverse the swampy terrain.
The Rebels were better equipped for the conditions, and the Imperials suffered from various technical problems with their battleskiffs and spacetroopers. The battle went stalemate for a while with heavy casualities on both sides.
Realizing that they probably would not stand a chance in the end, the Rebels initiated an evacuation process. And the battle developed into a desperate chase for the Rebel leaders, Krendan, Maidtha Fait, and Warl Thimbus and their respective squads before they could reach their transports.
Eventually, the Imperials managed to infiltrate the Rebel command center and destroy its shield generator which allowed the Dominator initiate a planetary bombardment, laying the Rebel base to waste.
The Empire emerged victorious, but at great costs. In addition several Rebel transport ships managed to escape the surface of he planet. These were pursued by the Dominator. Before the departure of the Star Destroyer, a team of Imperial troops were dispatched to the planet to find and desrtoy any possible remaining Rebel survivors. The operation developed into the Second Battle of Taul.
↑Uninvited Guests indicates that Taul was attacked as a result of information gleaned from the probe droids that were sent out to discover the main Rebel base, an event that occurred in Star Wars Episode V: The Empire Strikes Back with the Battle of Hoth. The Essential Atlas confirms that the Battle of Hoth occurred in 3 ABY.