All nearby Covenant forces, including a nearby corvette.
The Battle of Moscow was one of several large-scale engagements that occurred during the Covenant's invasion of Earth in late 2552. As a large industrial city that helped to produce arms and other supplies for UNSC forces the city was a prime target for the Covenant, whose ships smashed through the human defences with ease.
While the battle initially seemed to favour a Covenant victory, the timely arrival of a group of Spartans and ODST's turned the tide long enough for a full evacuation to take place, resulting in a great deal of the city being destroyed to eliminate an entire Covenant Legion. Though the UNSC were able to drive the Covenant from the region for some time, it did little to halt the ongoing invasion and played only a minor role in deciding the outcome of the Battle of Earth.
After their SOIEV pods ejected from the frigate UNSC Bright New Day, Sigma Team and Whiskey-04 landed not far from the Russian capital city of Moscow. Making their way onto Moscow to meet up, they found the city under attack by a Covenant Corvette. With defence forces being overwhelmed, the teams made their way into Moscow, and assisted in the evacuation of many citizens. With the Spartan and ODST reinforcements, morale was raised and the Covenant were momentarily pushed back.
However, the Covenant made a counter-attack. A column of wraiths moved along a bridge, and beat back the defenders until they were ambushed by several Spartans. Sniper fire eliminated many ground troops, but they were soon able to advance and eliminated a number of Marines. The Spartans of Sigma played an integral role in the conflict, assisting Marines and holding the line while the civilian evacuation took place. The wraiths, however, caused havoc among UNSC forces, demolishing buildings as they advanced. Kane-098 and Martin-A136, who had taken up a sniper post in a church tower, were driven out by plasma mortar bombardment, not before taking down several dozen brutes. The remainder of the Spartans had split up: Marco-035 and Jax-007 had reinforced a building to act as a fallback point, setting up heavy machine guns and LOTUS anti-tank mines while Louie-A199 and Alex-A121 ambushed the wraiths with a volley of missiles, destroying several before they and their Marine allies were forced to retreat.
Sergeant Major Mack and the surviving ODST's of Whiskey-04 attempted to flank the enemy, planting demolition charges. However, they were spotted, Raikov being instantly killed by a sniper and the others falling back. A brute Chieftan smashed Corporal Bell into the ground with a Gravity Hammer, nearly killing Mack, who was narrowly saved by Louie-A199, who shot the Chieftan several times before finishing it off with his combat knife. The battle was going badly on all fronts. Though they fought valiantly, the human forces were being slaughtered by the Covenant onslaught. It was only where the Spartans stood did the line hold. The civilian evacuation effort had been a success, however, most transports escaping safely. In an assault on the 'Last Stand' building, the remainder of Whiskey-04, barring Mack, were killed, while the Spartans ambushed and destroyed several more wraiths, blocking the path of the others.
Driving off yet another wave of Brute attackers, it became apparent that they would not win the battle on the ground. Sigma, along with Mack and what remained of the UNSC forces, fell back to the extraction zone half a mile away and were picked up by Pelican dropships. After boarding, it was revealed that a HAVOK nuclear warhead had been planted by Marines on the orders of HIGHCOM. It was detonated, annihilating the Covenant forces, along with a Corvette that had moved in over the city. About a third of Moscow was also destroyed in the blast.
In spite of the heavy price paid, the Battle of Moscow was seen as a victory for human forces on Earth, though the Covenant force in Russia was relatively small compared to the massive invasion in East Africa. The survivors were taken to ONI's PILLAR Base, located under Mount Everest. The Spartans received new MJOLNIR Mark VI armour to replace their heavily used and almost malfunctioning Mark V suits. After months spent with Sigma, Richard Mack Junior was transferred to another ODST unit in preparation for a new mission.