Train Eater - The Metal Gear Solid AU
Alternate title: "I Spent Three Hours Googling Trains To Make This As Period Accurate As Possible And Now My Search History Is Shot"
The Boss is a US Army 'General Pershing' steam locomotive, based on the US Army 101 locomotive that was in service for three wars.
Big Boss is an RSD-1 diesel-electric locomotive. Punished Snake is also an RSD-1 locomotive. But Big Boss is a model E1645 and Punished Snake is an E1646--two variations made for wartime production, but difficult to tell apart unless you know what you're looking for.
Solid, Liquid, and Solidus are all RS-2 diesel-electric locomotives, all built as 'successors' to the RSD-1. Solidus was made out of experimentally treated metal, but he oxidized faster than the others, making him appear older. This process took longer for Solid, but eventually caught up to him too.
Revolver Ocelot is a Russian locomotive class Ye, one of the many steam engines strewn across Soviet Russian railways during the Cold War. Unfortunately, he can't be a bullet train because it wouldn't fit the time period, and that would just be stupid.
Kazuhira Miller is an interesting case, but I figured it out. He is an 'American' locomotive built during the Meiji Era in Japan. That is actually a thing they did, so I get to use it.
Metal Gear is the SS-24 Scalpel, the only train in existence known to carry and launch ICBMs.