Otto fuel II is a monopropellant used to drive torpedoes and other weapon systems. It is not related to the Otto cycle. Otto fuel II was developed by US Navy in the 1960s for use as fuel in torpedoes. Otto fuel II was invented by Otto Reitlinger in 1963 (although tests with the substance had taken place before, for example in 1960 [1]); it is named after Reitlinger and for being the second iteration of the fuel (sometimes it is known simply as Otto fuel). The first torpedo to use it was the Mark 48 torpedo in the 1960s.