Complex sentence: Although it is a current and authorized rank, no U.S. Navy officer presently holds it, with the last living U.S. Navy fleet admiral being Chester W. Nimitz, who died in 1966.
Split into simpler sentences: Although it is a current and authorized rank, no U.S. Navy officer presently holds it. The last living United States Navy fleet admiral was Chester W. Nimitz, who died in 1966.