The AN/SPG-51 is a tracking / illumination radar for RIM-66 Standard missiles. It is used for target tracking and Surface-to-air missile guidance on Virginia-class cruisers, California-class cruisers, and Kidd-class destroyers. The French Cassard class frigates and Royal Netherlands Navy Tromp class frigates also utilise this system. Older variants were used on Charles F. Adams-class destroyers.