Produced for a short period of time only in the late 1950s, reference 5510 notably features a big crown with no crown guards. Some examples were chronometer certified, while others displayed "Submariner" along with the depth rating - these variants are known as "Two Liners". In production for a few years only, reference 5510 is instantly recognizable and characterized by its black lacquer ‘Swiss’ dial, lack of crown guards and 8 millimeter Brevet ‘big’ crown. Research suggests that reference 5510 was made in an exceedingly small series of less than 300 examples.