M531

M531 refers to a designation that can apply to several different entities, most notably a type of armored personnel carrier and a specific missile. The M531 Armored Personnel Carrier (APC) was a prototype vehicle developed by the United States during the Vietnam War era. It was intended to provide a more survivable and mobile platform for infantry compared to existing designs. While it underwent testing and development, the M531 APC did not enter mass production or widespread service. Its design incorporated features aimed at improving protection against small arms fire and artillery fragments.

Separately, M531 can also denote the AIM-54 Phoenix missile, a long-range, active radar-guided, air-to-air missile developed by the United States for the U.S. Navy. The AIM-54 Phoenix was designed to engage multiple targets at extended ranges and was famously carried by the F-14 Tomcat fighter aircraft. Its development began in the 1960s, and it saw service for several decades. The missile was characterized by its large size and powerful radar seeker. It was primarily used for fleet defense and air superiority missions. The designation M531 is less commonly used in reference to the missile than its official designation, AIM-54.