novelist,

The IS has former members of Saddam's army, but probably more relevant they have former members of the Syrian Army. Additionally the different terrorist groups have members from various militaries to include Pakistan and even some western armies. Finding folks with the expertise to teach someone to use the various pieces of ground equipment, or simply looking that up online, shouldn't be too hard. Gaining expertise (practice) is another thing, and then using all that equipment together in a combined arms fashion is another thing altogether. Reports indicate they're employing a combined arms approach, so to me that indicates that some rather senior former military leaders are instrumental in this movement. Maybe not, but it looks like, and smells like that is the case.

For everyone else if you haven't seen the PBS special it worth the 90 minutes to watch it.

http://www.pbs.org/wgbh/pages/frontl...ampaignId=1000

Losing Iraq

Also worth reading:

http://www.pbs.org/wgbh/pages/frontl...ampaignId=1000

Inside the Rise of ISIS

According to the author this situation would have happened regardless of whether the uprising in Syria happened or not.

That process, as far as I’m concerned, actually began as early as mid-to-late 2009. It was at that point that the Islamic State was in some ways forced to devolve into a typical terrorist organization. At that point it relocated much of its central leadership to Mosul [Iraq], which was a relative safe zone, and it was at that point that it essentially began its period of recovery.
The “Soldier’s Harvest” campaign has been the second of two 12-month campaigns. The first one was the campaign known as “Breaking the Walls.”

One of the primary objectives of that operation was to re-establish sources of leverage against security forces. A lot of that was done through a very significant campaign of intimidation — including collecting local intelligence on the addresses and family details of local security forces across the country.

A secondary objective of that initial campaign was the breaking out of prison of not only ordinary Islamic State foot soldiers, but most importantly, senior leading commanders, who’d been in prison for the final year or so of the U.S.-led surge in Iraq.