It was created in the 1970s with the reference 1655, being very similar to the GMT Master, except having a fixed bezel. This watch was made especially for speleologist (cave diggers) who easily loose track of time, whether it would be morning, afternoon, evening, or night. So it was that a 4 th hand was introduced which rotated once every 24 hours. It has a 4 th hand that indicated whether it is AM or PM. This hand would indicate to the cave diggers if it was 5 in the afternoon or 5 in the morning. However, the Rolex Explorer II became more popular with pilots or air traffic controllers than with speleologists.

All Rolex Explorer watches (we only mean Rolex Explorer I) come with NO DATE, and the case measures 36mm. The dial has a black background with a luminescent triangular marker at the 12 o'clock and luminescent Arabic numbers and a smooth bezel .

This model was designed especially by Rolex to be used for the Artic expeditions or to be used to climb high altitudes. It was tested by Rolex in the first expedition to the top of Mount Everest in 1953.