Insurrection of 2494
From Halopedia, the Halo wiki
The first Insurrection of the Eridanus Rebels, they took control of the word of Eridanus II. Two years later a UNSC Battlegroup arrived to put down the insurrection, though it cost them four destroyers. However, the rebel base hidden amidst the system's asteroid belt was never found. In 2513 there was another insurrection, which was put down by Operation: TREBUCHET.
Sources
Halo:The Fall Of Reach, pages 17-18.
