The Battle for D6, also known as the Battle for the Bunker, was a major battle in the Red Line's plans to control the whole Metro. It takes place as the final level in Metro: Last Light, save for the endings, and, in either ending, ends with the Rangers victorious (pyrrhic or not). The level itself is called D6 and is mainly a wave assault level.
The events leading up to the Battle began when the The Rangers of the Order discovered D6 under the main Metro as part of the secret Metro 2 line and occupied it. Despite the Rangers attempting to keep its existence a secret, the rest of the Metro found out and were interested. Rumors came out that D6 was full of weapons, food and medicine, enough to sustain the Metro forever. As a result of these beliefs, other factions of the Metro felt the Rangers were being greedy - hoarding such wonders for their own good.
All three major factions had plans to claim D6 - Hansa wanted to use diplomatic pressure (most likely threatening to stop supplying the Rangers) in return for a piece of D6; the Fourth Reich had a plan called Operation: El Dorado, devised by the Führer to attack and take over D6; and the Red Line's plan, which is the focus of Metro: Last Light.
Unbeknownst to the Rangers, the Red Line had a double agent working for them inside D6 - Lesnitsky. He worked in D6's science labs, so had direct access to the bio-weapons found there. It is likely he was a sleeper agent long before the Rangers even found D6, since it would take a long time for the Rangers to fully trust him. Under the command of General Korbut, he stole a bioweapon from D6, ransacked his own office to make it look like he had been kidnapped, and escaped to the Red Line. His ruse worked, as shown by Uhlman's conversation with another Ranger as to the whereabouts of Lesnitsky.
Safely back with his Red Line allies, Lesnitsky and Korbut tested the bio-weapon's destructive powers on an innocent station - Oktyabrskaya (the level Contagion) - and sent in troops to execute the infected, under the pretense that they were stopping the infection spreading. They successfully occupied the destroyed half of Oktyabrskaya and were only stopped from penetrating the Hansa Ring section by Hansa troops. However, the weapon had proven itself to be powerful and lethal - it would wipe out a station's population quickly, then go inert ready for invasion by the Red Line. The Reds now had a method of conquering the whole Metro, but they needed more of it - and only D6 contained more samples of the bio-weapon.
Korbut's forces advanced on D6, while Secretary Moskvin stalled the Rangers at the Polis Peace Conference. However, thanks to the Baby Dark One revealing his plans to everyone present, the Rangers had enough time to rush to D6 and set up a defense before the Reds arrived.
Metro: Last Light Edit
Using the Metro 2 train, the Rangers quickly made it to D6, Artyom, Khan, Miller and Uhlman among them. After a rousing speech from Miller, the Ranger forces moved to the front of D6 and the doors of the entrance sealed behind them.
The battle began with Red Line forces breaching the tunnel opposite of the Ranger defensive lines and deploying heavily armored Red Line troops against Artyom and the other Rangers, with both sides taking heavy casualties and the first line of the Rangers being forced to fall back to a secondary defensive position. Despite heavy losses and Artyom being injured, the Rangers managed to defend the platform against the Red troops long enough for their forces to regroup against the next attack.
However the Ranger defenses in the parallel tunnel were overrun by a Red Line armored Rail Car, a tank. Armed with a heavy machine gun and rockets, and protected by thick layers of metal. The Rangers' small arms could not damage it, however Artyom, armed with a Preved anti-tank rifle, managed to destroy the tank by disabling it's wheels and detonating the ammo stores. The resulting explosion killed the remaining Red Line troops in the vicinity. While the tank had been defeated, the Rangers had taken severe casualties and were forced to fall back to the final defensive position before D6, to await the oncoming onslaught.
With only a few Rangers left, the Red Line attempted to overrun their position with heavily armored shock troops. Artyom, utilizing a ramshackle Gatling emplacement, defeated these troopers with relative ease. Finally, the Reds sent in their heavy trooper - a flamethrower wielding brute defended by riot shield armed guards which nearly succeeded in breaking through the Rangers' defenses, however the Rangers manage to rupture the fuel tanks of the flamethrower which then exploded, taking out the heavy trooper and his retinue of guards. The Rangers allowed themselves a moment of celebration before the sounds of more advancing troops echoed up from the tunnel. Knowing that holding their position against another wave of enemy troops will be impossible with the remaining Ranger forces, Miller then reveals that D6 has been rigged to explode in case the Rangers fail to defend the bunker, and that D6 contained no ammunition, no medicine, no food, - no miracles; only more and more bio-weapons. Their predecessors from before the apocalypse ironically left only more death, and Miller knew that with such an arsenal, it would only be a matter of time before it destroyed the whole Metro.
But the Reds had one final card left to play. Seeking a swift end to the conflict and to demoralize any remaining defenders, the Reds sent their armored train into D6, which destroyed the entire defensive line and breached the walls of D6. The crash scatters the surviving Rangers, killing many and severing Miller's legs, leaving the lightly injured Artyom as the only Ranger left capable of fighting. The leader of the Red Army, Korbut, taunts Miller, claiming victory after disembarking from the train and summarily executes Uhlman, but Artyom began crawling towards the self-destruct panel, reaching it before Korbut or his forces can restrain him.
In the standard C'est la Vie ending, Artyom pulls the lever and D6 detonates. The Red Line troops frantically try to escape, but are all caught in the explosion. The Rangers too, sacrifice themselves to save the Metro. In the moral and canonical Redemption ending, just as Artyom is about to pull the lever, the Baby Dark One appears and tells Artyom he can let go. The other Dark Ones appear, having been set free by the Baby Dark One, and they attack the Red Line troops, killing Korbut and many others, leaving the rest to flee. D6 has been saved and Artyom has finally been forgiven, in his eyes, for what he did on Ostankino Tower.
In the years following, it is revealed that life has continued in the Metro, thanks to the actions of Artyom and his fellow Rangers. The Dark Ones, regardless of which ending was chosen, leave the Metro, although it is speculated that they will return one day.
Metro 2035 Edit
The events of the battle go somewhat differently in Metro 2035. The location of the battle is never called D6, but simply referred to as "the bunker". Since the little Dark One isn't part of the canon of the novels, it's likely that the Rangers managed to repel the Red Line's assault through conventional methods. Artyom claims that the Red Line battalion had between 300 and 800 men fighting during the battle and confirms that they were led by Czeslav Korbut, their objective being the chemical weapons stored inside the bunker. It is also revealed that Hunter took part in and survived the battle. Artyom fought alongside his friend, Letyaga, who was seriously injured and pronounced dead by blood loss. Both he and Artyom share the same blood type (A Rh Negative), to which Artyom gave him a 1.5L of blood for; thanks to this Letyaga made a full recovery. Miller lost his arm and became crippled during this battle, though this contradicts what he told Hunter in Metro 2034.
In either ending, the Dark Ones leave Moscow completely to an unknown destination, promising Artyom or Anna they will return one day to help rebuild humanity. The Baby Dark One waves goodbye to Artyom or Anna, and accompanies his family out of the city.
In both endings too, the Red Line army and Korbut are destroyed, leaving the Red Line weakened.
In the C'est la Vie ending, all of the Rangers die and D6 itself destroyed. Anna survives and gives birth to Artyom's child. Years later, Anna tells their child about Artyom and how he saved the whole Metro.
In the Redemption ending, with the Rangers being saved by the Dark Ones, Miller - now confined to a wheel chair - begins training new Rangers in Polis. Uhlman is said to be killed in the battle, and Khan disappears afterwards, leading to much speculation on Artyom's part. He suggests that he simply 'moved on' - left D6 for somewhere else in the Metro, or perhaps he accompanied the Dark Ones on their journey. Artyom also continues as a Ranger.
Metro 2035 reveals that despite the Red Line being weakened by the war, General Moskvin was able to hold onto power. The book also tells us that the Spartan Order lost 50 men in the battle and they had to make a deal with Hanza, who was the only one capable of providing highly trained men to replace their losses. Miller still feels sorrow over the heavy casualties that the Rangers suffered during the battle and regularly drinks in honour of his fallen comrades. Artyom and Anna left the Order after the battle, moving over to VDNKh to try and live a peaceful life, in spite of Miller's protests.