(This story appeared on Slashdot apparently and someone emailed me about it so...)
The US Air Force is testing new transparent armor made using aluminum oxynitride (developed by Raytheon and trademarked ALON®).
Transparent aluminum compounds are neither new nor unusual. Corundum (aka aluminum oxide) is the base substance of ruby and sapphire (which differ only in impurities), both of which are currently used for armor coatings in military/police equipment. If you need to see through something and not have bullets or shrapnel destroy it, chances are aluminum is involved. (See here for a ~600Kio PDF with lots of technical details about aluminum compounds used in transparent armor.)
AFDBs will develop a natural coating of aluminum oxide with exposure to air, so paranoids are already protected. (Paranoid seniors: try abrading your beanie and quickly sprinkling it with chromium dust for a stylish ruby coating.)
The testing of ALON® for military purposes is not new either. Here's a press release from 2002 announcing an agreement between Raytheon and Surmet Corp. to develop and market ALON® products commercially for the first time, whereas previously it was "developed as advanced military material and kept as a well guarded secret" (Warning: the terms "synergy" and "commercialization engine" are leveraged, although with the last one they had enough shame to put scare quotes around it.)