Designed to show the time in two time zones simultaneously, the GMT- Master, launched in 1955, was originally developed as a navigation instrument for professionals criss-crossing the globe. Instantly recognizable with its two-colour 24-hour graduated bezel – although single-colour on a few variations – The GMT-Master became the favourite watch of pioneering aviators and would later contribute to some of the greatest aeronautical achievements, as well as accompany astronauts at the height of the space age.