I was on a tractor forum looking through posts and found these two links that I thought I would share here. They are US Army manuals online. The first one is on hydraulics and the second one on welding. It even covers forge welding so it is on topic. 
I haven't had the time to read much of either link yet. But I will very soon!
Ric
Army Hydraulics Field Manual
Army Welding Field Manual

I haven't had the time to read much of either link yet. But I will very soon!

Ric
Army Hydraulics Field Manual
Army Welding Field Manual