In the contemporary advertisements, Omega made much of the depth testing on these watches, both in the field but also in the lab.
The cases were routinely hydrostatically tested to 60ATM and shock tested (500g weight dropped onto a running watch from 25cm).
In one test the watch was taken down to 1370m using hydrostatic pressure and it was reported that it only stopped at that 'depth' as the crystal had deformed to the extent that it was resting on the seconds hand, so stopping the watch from running. Interestingly, this failure can be partially attributed to the design of the case sealing, which whilst superior for the advertised 600m rating, would not be correctly designed if going beyond 1370m.
Looking at the design, the crystal rests on a large ring 'insert' (actually made of two interlocking parts - one being plastic, one steel) that in turn rests upon a seal against the back of the watchcase. When the crystal is fitted it, the ring and seal are compressed and the seal squashes to isolate the case interior. However at great depth there is extreme pressure and this arrangement can continue to compress as the seal (and to some extent the plastic part of the ring) is by nature not solid. This has the effect of moving the crystal closer to the hands. Had that insert been made of one solid piece of steel and be resting on a machined surface at the back of the watch, then the Ploprof would undoubtedly have been able to achieve a greater depth. When you read that, do you recognise the design we've just outlined? Yes its called a Rolex Sea Dweller Deep Sea.... Its nice to see Rolex basing the new model of their original Ploprof competitor on the original Ploprof design, what goes around....