How to Tell Apart the Rolex Explorer and the Explorer II?

The two models we are going to talk about share a lot of similarities, but the Explorer and the Explorer II models are very different Rolex watches. If you have no idea of their difference, let’s read on to find out the answer.
Rolex released the Explorer watch as a tribute to one of mankind’s most significant expeditions in 1953,—Sir Edmund Hillary and Tenzing Norgay’s ascent to the summit of Mount Everest, the planet’s highest mountain. Aptly named the Explorer, the replica watch featured solid stainless steel construction, a highly legible dial, and a waterproof case also resistant to temperature swings. 
In 1971, Rolex launched a new model they dubbed Explorer II. This time around, instead of marketing it to mountaineers, the Explorer II watch targeted spelunkers and polar explorers—i.e. adventurers that spend a lot of time in the dark or in areas with irregular sunlight hours. As such, the Explorer II offered an extra 24-hour hand, a 24-hour marked bezel, and a highly luminous dial so that wearers could always differentiate between day and night hours regardless of their surroundings.
As for functionality, the Explorer and the Explorer II are different a lot. The Explorer is a simple time-only Rolex model with center hour and sweeping seconds hand.
What’s more, the Explorer II includes some other complications. First, there’s a date window at 3 o’clock. Then there’s the extra 24-hour hand on the dial. It’s important to note that on the inaugural Explorer II, the ref. 1655, this extra triangular-tipped hand was simply an AM/PM indicator since it’s synced to the main hour and minute hands.
The Explorer II started its life as a 36 mm Rolex watch and continued as such for decades until the introduction of the ref. 214270 in 2010, when the watch grew to 39 mm. On the contrary, the Explorer II started as a 39 mm fake Rolex watch, then grew to 40 mm with the 16550, and finally grew again to 42mm with the ref. 216570.
The Explorer is decorated with a black dial with 3, 6, and 9 numerals sitting alongside stick/baton indexes. As a matter of fact, this dial design is referred to as the “Explorer-style” dial.
While the first Explorer II ref. 1655 was only available with a black dial, Rolex gave both black and white dials on all subsequent Explorer II references. The extra 24-hour hand started as orange, then Rolex changed it to red before changing it back to orange on the newest version.
No matter which model you prefer, both the Explorer and the Explorer II are Rolex replica watch icons that seamlessly marry utility, durability, and looks.