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Introduced in 1957, the OMEGA Automatic Seamaster 300 was advertised as specially designed for professional and amateur divers, with water resistance to 200 metres and a rotating bezel for tracking dive time. Its name came from performance beyond contemporary testing devices, thanks to a high-resistance crystal and crown. It used calibre 28 SC-501, a matt black oxidised dial with luminous markers and radium-coated hands, and a Seahorse medallion caseback; French diver Alain Julien praised its robustness after daily wear in 1958–59, logging more than 1,500 dives.