The First Battle of Arcadia saw the UNSC Marine Corps holding the defensive line around the planet's major population centers to allow the evacuation of the civilian population with the assistance of the Spartan-II Red Team. After receiving reinforcements and repairing the base, the Marines fought through a sizable Covenant garrison force in an attempt to secure a mysterious Forerunner structure in the region. Forge rallied scattered marines, who quickly retook it from the Covenant. However, during the patrol, Covenant forces under the command of a Covenant Arbiter overran and nearly destroyed the base. A reconnaissance force led by Sergeant John Forge was deployed to survey the area. At the final stages of the campaign, the Marines quickly established a base of operations in Harvest's arctic region. Not long after the First Battle of Harvest, the Corps experienced its first major encounter with the Covenant at numerous engagements throughout the Outer Colonies, including the Harvest Campaign, eventually lasting from 2526 to 2531. Main articles: Harvest Campaign and First Battle of Arcadia During the battle, Captain Ponder became the Corps' second casualty of the war. At the event, only three Marines were present, one officer and two NCOs, training the planet's Colonial Militia. The UNSC Marine Corps' second encounter with the Covenant was the First Battle of Harvest in 2525. The wound was minor, however, and he survived. The first casualty was Staff Sergeant Byrne, who was stabbed in the leg with an energy cutlass. Staff Sergeants Avery Johnson and Nolan Byrne were waiting, expecting to find Insurrectionists boarding the vessel, only to see four Kig-Yar raiding the ship. The Battles of Harvest, Arcadia, Sigma Octanus IV, Earth, and countless others saw fierce fighting between Marines and the Covenant Army.ДЇirst contact with the Covenant was aboard a shipping vessel. Human-Covenant war Main article: Human-Covenant warДuring the course of the Human-Covenant war, the Marines played a central role in maintaining a defensive stand as well as assaulting several Covenant base of operations.

Marines were highly utilised during Operation: TREBUCHET. Later, the UNSC Marine Corps would be responsible for dealing with Insurrectionist uprisings among UNSC colonies star systems. It only gained prominence out in other systems after the CMA's fall from grace. When the UNSC began expanding in the 24th century, the Marine Corps was retained within the Sol system. After the United Nations claimed victory in 2164, it reorganized into the UNSC, thereby changing the UN Marine Corps to the UNSC Marine Corps. The UN Marine Corps (predecessor of the UNSC Marine Corps) was one of the primary combat groups fielded by the UN in the Interplanetary War, and were the first military organization deployed offworld in 2163.

Shadowrun free marine corps