The process can be simple and easy, or very complicated. For instance, I was recently asked to go to Iraq and agreed. That got bogged somewhere so Iraq is out unless I go alone, which will probably do in 2010. There is no standard.
As of today, this is the first set of paperwork for Afghanistan. Minutes ago, I completed and emailed these forms to Afghanistan for an embed with the Stryker Brigade. Looking forward to getting back with the infantry: