[gsquaredxc]

There's some good answers here but something important is missed. Militaries spend a lot of time having soldiers shoot rounds down the range to ensure everyone is up to snuff. The engineering corps is similar but better. You can fund target practice for your army engineers by having them go build public infrastructure. It's a win for the military (practical experience), win for locals (public infrastructure), and a win for the taxpayer (two for one deal).

[bumby]

I don't think that idea necessarily holds for the Army Corps of Engineers. They technically work under a military command, but the vast bulk of the engineers are civilians. The military officers tend to rotate in and out of positions relatively fast. And the civilians aren't required to do construction in combat theaters (although voluntary positions do exist). So the idea that the USACE is set up to give practice for military theaters isn't really apt. It's more about the scope and incentives of the projects they work on. E.g., a private company doesn't have the right timeline or profit incentives to build dams for flood control.