Battle of Vilcan

The Battle of Vilcan was a major ground engagement during the Great War in the Dermkha Front beginning in June 2641 and ending with the August Ceasefire of 2647. It is considered to have been the longest battle in history. It was the first ground engagement of the Mirdesh forces, who along with their Surben allies faced off against the invading combined forces of the Dermkha State and Terran Federal Republic. Ultimately, though the Terrans achieved control of a majority of the planet by the end of the war, several major cities were retained by the Coalition forces by the battle's conclusion. 
The battle is significant for its length and relative success of allied forces, which were generally unable to match the Terrans on the ground throughout the war. Additionally, Terran reliance on heavy bombardment irreversibly changed the planet's ecosystem, with large regions of the central and western continents reduced to wastelands. It is estimated the Terrans dropped over sixty billion artillery shells on the planet over the course of the battle, which when combined with aerial and orbital bombardments amounts to over 147 yottatons of TNT. The Terrans also made widespread use of mechs which proved to be highly capable in their elite configurations. HERAKLES brigades were deployed on more occasions on Vican than all other instances combined, for a total of 37 deployments on Vican, all of which were decisive victories.
The codename of the invasion by Terran forces was Operation Obsidian Morningstar.