The Siege of Storm's End was an important engagement in Robert's Rebellion. Lord Robert Baratheon's army had been driven from the south by the forces of Mace Tyrell, leaving the Stormlands largely unprotected. Robert named his brother Stannis the Castellan of Storm's End to hold the castle until his return.
Stannis was young and untested in battle, and most expected him to surrender when the Tyrell army laid siege to the castle. Paxter Redwyne's fleet had sealed off Shipbreaker Bay to any ships that might try to supply the beleaguered defenders. Stannis proved stubborn, however, and he held Storm's End through a full year of siege, despite the fact that his own men were starving. They were nearly forced to eat their own dead.
Fortunately, before they were forced to that extreme, a notorious smuggler named Davos sailed through the stormy bay and right past the Redwyne ships to land under the castle. The food he brought allowed the garrison to survive long enough for Eddard Stark to lead a rebel army to their defense. There proved to be no battle; the Battle of the Trident had already been fought, and as soon as the rebels appeared on the field, Lord Tyrell surrendered.
Davos was knighted for assisting the garrison, but Stannis decreed that he must lose one joint from each finger on his left hand for his years of smuggling. Forthwith, Davos was known as Davos Shorthand, and took the name Seaworth for his new house.