According to Use of Ceramics Is Critical To Pentagon’s War Goals, ceramics are replacing steel for both personal body armor and vehicular armor:
Elite American units such as the Delta Force have been wearing ceramic armor — about half as heavy as the metal variety — since the mid-1990s. Now more U.S. ground forces will get it.
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As depicted in the movie Black Hawk Down, U.S. soldiers removed the metal plates from their body armor because it weighed them down too much for urban fighting, leaving them vulnerable when local militiamen attacked with gunfire.