How to begin decompiling and reverse engeniering an old game

[Vasim]

Hi, lately I've had on my mind an old game called Tom Clancy's Ghost Recon (2001), it isn't very popular and I wanted to see if I could try and update it's engine to at least have some more up to date functions, like the basic function of seeing your own weapon at least.
Biggest problem is that, I don't have ANY information on it's engine,I'm left to assume that is is entirely custom and made only for GR2001, so I wanted to ask if any of you had learning resources or anything of note that could help me start reverse engeniering it,I know programming,but not the latter.
Any help you could give me be it a hint, some tangential information or a book even,would be much appreciated.

[Halamix2]

There is this topic which is similar: viewtopic.php?p=675

[WinFan3672]

I will say that, if you want to do it, you need:

• Deep knowledge of x86 assembly, the C compiler, the build toolchain, debugging, and much more. This isn't the kind of thing the average soydev is going to be able to do.
• Several kilograms of patience. Decomp takes years, even for teams of people. Hell, the LEGO Island decomp has been going for what, a year now, and that is a significantly older game, and even that is really early days.
• The realisation that 100% accurate decomp is basically impossible for such a large project
• The realisation that demand for decomp is extremely low for such a game (sorry)

Also, that game likely runs on some kind of game engine, so you'd need to start there, be it to get a copy of it or to reverse-engineer that.