From Halopedia, the Halo wiki
On October 10, 2552, Battle Group Rhino detected twelve unidentified large vessels in the Sol system broadcasting outdated civilian IFF codes. Upon approach, eleven of the vessels made unauthorized slipspace transits from the Sol system. Pursuant to standing orders to engage vessels not positively identified as friendly, Battle Group Rhino moved to engage the remaining ship. The UNSC Totem Lake was subsequently lost with all hands after reportedly suffering multiple hull breaches and boarding parties. The battle group, under the direction of Murray, then disengaged and regrouped at Phase Line Alpha above Enceladus. Vice Admiral Williams, in charge of the entire Third Fleet, requested permission from Fleet Admiral Harper to attack the ship, but permission was denied. Following these events, Captain Murray reported them on October 17 in the form of 83 files later termed Log 01-0991. The data mainly served as an after-action report for the loss of the Totem Lake in what came to be known simply as the Battle of October 10.