Armstrong was a lieutenant in the US Navy Reserve. He originally joined in 1949 and received training at the Naval Air Station Pensacola to become a pilot. He flew 78 missions in the Korean War — a total of 121 hours in combat. He left the navy to complete his space engineering degree and masters before joining NASA.
But he always remained a navy man. Perhaps that's the reason why he chose to be buried at sea. Or perhaps it's because he was such a humble and private man. According to Secretary of the Navy Ray Mabus, "he never wanted to be a living memorial, and yet to generations the world over his epic courage and quiet humility stands as the best of all examples." [CBS]