1....preferably artillery or intelligence.
Grant turned a number of the heavy artillery regiments defending Washington into infantry because he needed the latter more than the former. It proved quite a shock to those who thought they'd found a relatively safe berth to serve in.
And they often got overrun, had sh**t blow up in their face, had to lug around heavy sh**t, deal with horses and probably a dozen other horrible things I don't know about. I'd want to do it for the cool engineering involved, the math and the BOOMs, not for the safety.
Poll
