This paper discusses the development of an improved assault amphibian personnel carrier, the LVTPX12, for the U.S. Marine Corps. The design problems encountered and the methods used to solve them are described. The development program included the design of a new lightweight, high performance transmission and a compact, fully enclosed, powered armament station. The vehicle is constructed of aluminum armor and is diesel powered with water jet pumps for water propulsion. Prototypes are undergoing pre-production tests.