Where exactly does this game stand on the timeline? I only just realized that Snake and Solid snake aren't the same guy so I'm pretty confused. I'm guessing this is just before the original Metal Gear, where Big Boss is fully into his obsession with soldiers and developing his crazy merc nation?
Game, Year, and Protagonist are as follows:
Metal Gear Solid 3 Snake Eater, 1964, Naked Snake/The Man Who Will Be Big Boss
Peace Walker, 1974, Naked Snake/Big Boss
MGSV Ground Zeroes, Later In 1974, Big Boss
MGSV The Phantom Pain, 1984, Big Boss
Metal Gear, 1995, Solid Snake
Metal Gear 2: Solid Snake, 1999, Solid Snake
Metal Gear Solid, 2005, Solid Snake
Metal Gear Solid 2 Sons of Liberty, 2007-2009, Solid Snake & Raiden
Metal Gear Solid 4 Guns of the Patriots, 2014, Old Solid Snake
Metal Gear Rising Revengance, 2018, Raiden
I'm also trying to figure out Codenames and ranks. On the rescue the engineer mission I went loud and mowed down a squad of dudes outside the prison but got an S rank cause none of them actually died. And my codename was still Chick, as it's been every single time.
Codenames are dependent upon your behavior more than your rank, though they sometimes overlap. Check the database tab in the iDroid, it tells you most of their criteria. Rank is just dependent upon points, and because ALL FOR REVENGE killing people no longer directly reduces rank, though it does lose you certain bonuses.