From OpenwaterpediaRolex Oyster in 1926 and promoted it through Mercedes Gleitze's well-publicized swim across the English Channel as proof of the reliability of the The Oyster watch.
Gleitze Testimonial to Wilsdorf
You will like to hear that the Rolex Oyster watch I carried on my Channel swim proved itself a reliable and accurate timekeeping companion even though it was subjected to complete immersion for hours in sea water at a temp of not more than 58 and often as low as 51. This is to say nothing about the sustained buffeting it must have received. . . . The newspaper man was astonished and I, of course, am delighted with it.