In Star Trek IV there is made mention of transparent aluminum. Very cool idea, huh? Well... science and engineering have nearly caught up with that science fiction material. It's aluminum oxynitride that the US Air Force is testing for transparent armor:
ALONtm is a ceramic compound with a high compressive strength and durability. When polished, it is the premier transparent armor for use in armored vehicles, said. 1st Lt. Joseph La Monica, transparent armor sub-direction lead
"The substance itself is light years ahead of glass," he said, adding that it offers "higher performance and lighter weight."
Traditional transparent armor is thick layers of bonded glass. The new armor combines the transparent ALONtm piece as a strike plate, a middle section of glass and a polymer backing. Each layer is visibly thinner than the traditional layers.
ALONtm is virtually scratch resistant, offers substantial impact resistance, and provides better durability and protection against armor piercing threats, at roughly half the weight and half the thickness of traditional glass transparent armor, said the lieutenant.
In a June 2004demonstration, an ALONtm test pieces held up to both a .30 caliber Russian M-44 sniper rifle and a .50 caliber Browning Sniper Rifle with armor piercing bullets. While the bullets pierced the glass samples, the armor withstood the impact with no penetration.
In extensive testing, ALONtm has performed well against multiple hits of .30 caliber armor piercing rounds -- typical of anti-aircraft fire, Lieutenant La Monica said. Ttests focusing on multiple hits from .50 caliber rounds and improvised explosive devices are in the works.
Thanks to Ry for the email on the topic.