John Francis Lehman Jr. is an American private equity investor and writer who was secretary of the Navy (1981–1987) during the Reagan administration in which he promoted the creation of a 600-ship navy.

The 600-ship Navy was a strategic plan of the United States Navy during the 1980s to rebuild its fleet after cutbacks that followed the end of the Vietnam War. The plan, which originated with Republican leaders, was an important campaign plank of Ronald Reagan in the 1980 presidential election, who advocated a larger military and strategic confrontation with the Soviet Union.