A few decades ago, Rolex deducted a version of the Air-King ref. 5500 with the Explorer’s dial. Because of that, this special model is often regarded as the Rolex Explorer. 5500, even though it has more in common with the Air-King line than the Explorer. It is a hybrid, combining the restrained Air-King case with the instantly recognizable Explorer dial. Just like the Air-King 5500, the Explorer 5500 features a 34 mm case, significantly smaller than the Explorer ref. 6610 and the Explorer ref. 1016 almost at the same time. 
Similar to the Air-King, the Explorer ref. 5500 is available in an exact and super exact version with the Calibre 5500. 5500 with the 1520 or 1530 movement. There are also ultra-rare “underlined” examples with a line under the “SUPER PRECISION” text. Even though they share the same silhouette, case, bracelet, and movement, they look very different because of their dial and hand designs. While the huge majority of Air-King models came with a light-colored dial with simple baton hands and bar indexes, the Explorer version featured the now iconic 3/6/9 black dial and fake Rolex’s popular Mercedes-style hands.
The Air-King 5500 was manufactured for over thirty years, while Rolex produced the Explorer 5500 for about ten years. Apart from that, the history and evolution of the Air-King 5500 are well documented, while there is still some mystery surrounding the Explorer 5500. It was once rumored that the Explorer 5500 was sold exclusively to military personnel through the British Naval, Army, and Air Force Research Institute.
With this in mind, there are many anecdotes of civilians buying from Rolex retailers in the UK and Canada in the 1960s to refute this theory. What’s more, the Explorer 5500 appears in at least one official replica Rolex vintage catalog, suggesting that it was available for sale to the public at some point in the production process.
The prices of the two Reference 5500 watches also differ a lot. the Air-King 5500 remains relatively affordable, starting at just under $4,000. The true original Explorer 5500s are much harder to come by, and when they do come up for sale, expect to pay at least five figures if you want to add them to your collection.
So no matter if it’s the understated Air-King or the intriguing Explorer, Rolex’s 5500 has long been a reliable and durable watch, despite its size. Besides that, whether you choose the Air-King version of the Explorer, you’ll get a timeless vintage watch with all of Rolex’s signature features.