If you care to go visit the Bull Simons Museum at Bragg, you'll find among the other goodies on display a PASGT K-pot *Fritz* helmet work by one of the US troops who went into Grenada on Operation Urgent Fury. At the time, the Kevlar brain buckets were so new that they'd not yet been certified for parachute drops, and those who jumped in did so wearing the old M1 steel helmet, then changed into the new K-pot.
One of the 82nd Airborne troops who did so later took a hit to the head from a 20 mm antiaircraft cannon'd direct fire, the high explosive shell hitting and detonating on his new K-pot, not surprisingly stunning him, but yet not wounding him fatally. The helmet was ruined but had done its job, and now sits on display to show the visitors how well our hardhats work...sometimes.
And indeed, a lot of guys became believers in the new head bucket after that, though some early Gen-Tex production versions suffered from delamination. They are now hopefully all out of the system.
I do not know if Tillman was wearing a K-pot, or if he was hit in the head by .50 fire. But I was told by someone who was there with 2/75 Ranger Bn. that fire from a .50 was involved, and until I am otherwise better informed, I'll stick with that.
Tillman was, I understand, on his third tour, having served tours in Iraq during Operation Iraqi Freedom in 2003 and in Afghanistan during Operation Enduring Freedom in 2004. From what I've been told, I do not think he made a *dumb rookie* mistake.
Whether someone else did or not, I'll leave to the investigators to figure out, to the satisfaction of their assorted bosses and masters. The future opinion of other various snakeeaters, castlewreckers and heartbreakers may be influenced by their findings, as by other things, but the word will get out, and it will be spread in that close community.
As it happens, I have been in that same museum and seen that helmet. But my recollection is that it was hit by small arms fire, not a 20 mm AA gun. Frankly, even if the .50 cal round was "stopped" by the helmet, I would expect the force of the impact to break the soldier's neck. Tillman may have been alive during the firefight, but I simply do not believe that he survived being hit by a .50 cal round in the head.