Who Is the only U.S. serviceman buried at the West Point Cemetery who died fighting under a foreign flag?

David "Mickey" Marcus is the only American serviceman buried at West Point Cemetery who died fighting under a foreign flag -- the flag of Israel, on 10 June 1948. He was the military advisor to the newly-formed Israeli army and was given command of organizing the Jerusalem front after the Arab invasion, and he was killed the day before a UN-imposed cease-fire took effect. Unfortunately, he was killed by "friendly fire" from an 18-year-old sentry (who had challenged him in Hebrew and didn't understand his response in English).
https://en.wikipedia.org/wiki/Mickey_Marcus

David Marcus was buried at West Point Cemetery in July 1948. He died fighting under the flag of Israel.

On a warm July day in 1948, a funeral was held at the U.S. Military Academy in New York for David Daniel Marcus, class of 1924. In many ways it was a typical West Point funeral, with a bugler, a firing party and a number of distinguished mourners. In one respect, however, the ceremony was unique. Although an American flag covered his coffin, Marcus was the first soldier buried at West Point who had died fighting under another nation's flag. Only two weeks before his death, he had been appointed the first divisional level field commander in the army of the fledgling state of Israel. Marcus was born on New York's Lower East Side on February 22, 1902. He was the fifth child of Mordecai and Leah Marcus, who had emigrated from Romania to escape the waves of antisemitism sweeping Eastern Europe at the end of the 19th century.

https://www.historynet.com/david-mickey-marcus.htm