This is the earliest version of the Rolex GMT-Master Ref. 1675. The Bakelite bezel that defined the earlier 6542 is gone in favor of the metal insert that will grace the 1675 for its entire run. This bezel has aged and faded significantly from its appearance when it was made. When I think of an early 1675, I think of something like this: a bezel insert with a pale baby blue section for the night and a soft, faded red for the day.
The very earliest example of the 1675 is the so-called “OCC” dial, with text below GMT-Master reading “Officially Certified Chronometer.” The OCC text is understood to reflect the use of the non-microstella 1535 caliber, though there have been some seen that actually do include the newer 1565 movement. Soon, with the formal introduction of the microstella-regulated 1565 caliber, we’ll see a shift to the “Superlative Chronometer Officially Certified” text.
The OCC dial is very similar to those found in the 6542 but slightly larger, so they are not exactly interchangeable parts. As with the 6542, this 1675 has a hyphenated “Oyster-Perpetual.”
Apart from the standard-issue aluminum bezel insert, another defining feature of the first steel 1675s, and indeed all subsequent ones, is the appearance of crown guards on the side of the case. These will evolve a bit here and there, but if a 1675 is made of steel, it’s going to have crown guards.