Rolex introduced the Explorer II series in 1971 to complement the Explorer line. It features an additional 24-hour hand like the GMT-Master but the bezel is fixed in place. This 24-hour indication, among other things, has been designed with regard to professional cavers, for whom a reliable temporal orientation independent of the outside world is of the utmost importance. Accordingly, at the design of the dial a special emphasis was put on excellent readability, even in the dark.
This original Explorer II Ref. 1655 used a 39 mm case, but this new Ref. 16550 has a larger 40 mm case. In keeping with its sporting intent, it used an Oyster bracelet and featured crown guards. The bezel is marked with numerals at even numbers between 2 and 24 and triangle markers between. The dial is similar to the contemporary Submariner with a large triangle marker at 12 00, large bar markers at 6 00 and 9 00, and smaller dots at the other hours. There is a date window at 3 00 with a cyclops magnifier. The hands are Rolex “Mercedes” style, with the 24 hour hand using an arrow point.
The design of this “transitional” Explorer II diverges greatly from the original Ref. 1655. The dial and hands are much more conventional, looking more like a Submariner or GMT-Master than the old model. The iconic huge orange triangle shaped 24 hour hand is also gone, as is a great deal of lume from the dial. And the bezel is marked with triangles between the even hours rather than stick markers. One upgrade was the addition of a sapphire crystal.
Another novelty was the availability of a white dial in addition to black. The paint used on the white dial is prone to fading, making a cream color that has become very desirable to collectors. Along with the orange-handed Ref. 1655, this cream dial Ref. 16550 is the most desirable Explorer II today.