The Rare Earth elements enable a wide variety of defense technologies, which are critical to the national security of the United States. As essential materials in the manufacture and operation of defense and weapons systems, these materials are used in many forms from low-purity concentrates and natural mixtures of metal (mischmetal) to ultrahigh-purity compounds and metals.
Rare Earths are critical to many defense related applications including the following:
• Precision Guided Munitions which include both missiles and “smart” bombs – Rare Earths provide directional capabilities
• Lasers – Used in rangefinders, target designators, and target interrogators
• Detection devices for underwater mines
• Communications
• Aircraft – Used in a variety of aircraft control mechanisms as well as in high-temperature resistant ceramic coatings used in jet engines
• Displays –Most defense system components contain one or more display devices associated with control panels to display and quickly communicate data
• 
Radar Systems
• Coatings
• Optical Equipment
• Sonar – Rare Earth alloy is replacing piezoceramic materials in several devices
• Electronic Counter Measures
The link below provides more information on defense applications and the importance of the Rare Earths to our nation’s security:
Rare Earth Critical Strategic Materials used in Defense Applications (USGS 2005, PDF file 726KB)
Photo credits: Dept. of Defense