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 was enlarged for Ref. 16550 of 1985 with 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.
Like the “transitional” Explorer II Ref. 16550, the design of Ref. 16570 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 notable difference between Ref. 16550 and Ref. 16570 is the black outlines for the hour markers on the dial. This is particularly noticeable on the white dial version.
Like Ref. 16550, the 24 hour hand is independently adjustable, so the Explorer II can now display a second timezone. This Ref. 16570 was originally equipped with Cal. 3185, but was updated in 2007 with the new Cal. 3186 with the rugged and anti-magnetic Parachrom Blu hairspring. Later examples also feature the “ROLEX ROLEX” rehaut like many other Rolex sports watches.
Unlike its short-lived predecessor, Ref. 16570 remained in production for over two decades. Rolex redesigned the Explorer II in 2011 with an even-larger 42 mm case and a new movement, becoming Ref. 216570.