Released in 1971, the Rolex Explorer II is an oft-overlooked watch within the Swiss manufacture’s collection. Designed specifically for speleologists (that’s cave divers for the uninitiated) the watch is best thought of as a sibling rather than a successor to the original Explorer. The Explorer reference 16570 was first introduced in 1989 and remained in production until 2011. The watch shares many of the same characteristics as its predecessor, the 16550, but did have a few notable upgrades. A new calibre 3185 movement powered the reference, offering better accuracy and a quick-set hour hand. Also new on the white dial version were black outlines around the hour markers which gave the watch a striking look and the moniker “Polar Explorer”. Like many of the 5 digit Rolex sports references, the 16570 was produced over the time the watchmaker changed from tritium to luminova for the hands and hour markers. Examples of the watch made before roughly 1997 feature tritium paint which will gain a yellowish patina over time. Post-1997 watches have luminova on the dial and hands and will not fade or change colour.