the adoption of the oyster case and self-winding rotor facilitated tudor's move into the production of tool watches. the french navy (marine nationale) played a key role in the creation of a tudor diving watch providing "in the field" research and development. tudor launched its first diving watch in 1954, the oyster prince submariner, waterproof to 100 metres. this was increased to 200 metres in 1958. over the years the submariner line adopted various features such as the "big crown" and "snowflake hands" that have been reintroduced on tudor's diving watches of today. the french navy began using tudor watches in the mid-1950s. as of the late 1960s, it was buying them in bulk without bracelets so that all were worn with military-issued straps or those adapted by the wearers themselves. this continued until the mid-1980s. in 1964, tudor also began producing an oyster prince submariner specifically for the us navy. meanwhile, 1957 saw the launch of the tudor advisor, which incorporated an alarm complication. the first models used and adapted the oyster case to amplify sound. later in 1969 this was changed to a more ‘traditional’ alarm case with an external case back to increase the volume of the alarm.