Navy Medal of Honor types
There have been four design types of the Navy Medal of Honor. The Navy was the first to introduce the Medal of Honor. This decoration has been awarded to both Navy and Marine members since 1862. The first type was introduced in 1862 and was used until 1913. The Navy's Medal of Honor was the first approved and the first designed. The initial work was done at the Philadelphia Mint at the request of Secretary of the Navy Gideon Wells. The design prepared by the Philadelphia firm of William Watson & Sons was the design selected. The central design of Minerva repulsing Discord was symbolic of the Civil War and was used on three of the Navy types and was also used for the first two Army types
The third type referred to as the "Tiffany Cross" Medal was introduced in 1919. Prior to WWII the Medal of Honor could be awarded for both combat and non-combat actions. This rare Tiffany type was only awarded for combat actions. The legend in the center reads: UNITED STATES NAVY 1917-1918. It's not clear to me how many were awarded (somewhere between 7 and 27) - for action in WWI.
The fourth type is the modern and present version of the medal and was introduced in 1942. As far as I can determine, the first recipient was Chief Petty Officer John Finn for action early on Pearl Harbor Day (7 December 1941).