<Tr> <Th> Officer </Th> <Th> Service </Th> <Th> Highest rank </Th> <Th> Date of rank </Th> <Th> Historical significance </Th> </Tr> <Tr> <Td> William Westmoreland </Td> <Td> U.S. Army </Td> <Td> General </Td> <Td> 1 Aug 1965 </Td> <Td> Senior most operational officer of the Vietnam War . Omitted from some historical lists, since Westmoreland served in the later 20th century when the regular military seniority system had already been well established . </Td> </Tr> <Tr> <Td> Hyman G. Rickover </Td> <Td> U.S. Navy </Td> <Td> Admiral </Td> <Td> 3 Dec 1973 </Td> <Td> Head of the nuclear program of the United States Navy and one of the longest serving officers in United States military history . </Td> </Tr> <Tr> <Td> Colin Powell </Td> <Td> U.S. Army </Td> <Td> General </Td> <Td> 4 Apr 1989 </Td> <Td> Served as Chairman of the Joint Chiefs of Staff during the Gulf War . Later considered for five star promotion; however, a Congressional bill was never passed . Later served as Secretary of State . </Td> </Tr>

What is the highest rank in the american army