Seamaster 600 Professional models, also called "PLOPROF" for PLOngeur PROFessional, professional diver, was launched in 1970. The first series was marked "600" on the dial, while the second series was marked "600m/2000ft". It took over four years of study and research to design the model. The monocoque cases are made out of one piece of massive stainless steel and fitted with an extremely strong tempered mineral crystal and a special twin-locking crown.

The model was tested to a depth of 600 meters at the factory and to 1,000 meters in the Gulf of Lion off the coast of Marseilles where it was notably used by Jacques Cousteau during a series of experiments designed to test man's physical and psychological capacities to work at depths of around 500 metres.

During operation "Janus" in 1970 in collaboration with the renowned company COMEX, then the world leader in sub-sea engineering and in manned and unmanned sub-sea interventions, three divers wore the Seamaster 600 for four hours a day for eight days. It was also scrupulously analysed by the American diving research centre Ocean Systems Inc. in Tarrytown, NY, which concluded that, taking into account the appropriate proportions, the watch is more resistant than a submarine.

The "PloProf" is described and illustrated in Omega Saga by Marco Richon, pp. 136 & 137 and in Omega Watches by John Goldberger, pp. 150 - 152