This is one of the iconic 20th century watches, made by the watchmaker of the 20th century: the Rolex GMT Master. This model was originally developed for the airline Pan American World Airways (Pan Am), the excellent website GMTMaster has an account of the origin of this model: 

In the early 1950’s, Pan American World Airways had a growing cache of pilots traveling ever more distantly and frequently. As their time abroad grew, Pan-Am realised that supplying their pilots with a watch that tracked both local and home time could help reduce scheduling error, improve jet lag, and even help morale. They approached Mr. Rene-Paul Jeanneret, the public relations manager of Montres Rolex SA, and requested that they develop a dual time-zone watch for their fleet.
 
The Rolex GMT has a 24 hour hand (the red hand with the arrow) and a rotatable bezel, to read the time in a second time zone you rotate the bezel to the correct offset and then read the hour from the bezel. It’s a simple solution to a 20th century problem, one created by the appearance of the jet airplane. 

This particular Rolex GMT dates from 1961, s/n 694xxx making it an early model date coded on the inside of the case back to the second quarter of 1961. It has the first iteration of the crown guards, referred to as pointy-crown guards (PCG) because of their shape. The watch has a beautiful, original gilt dial (Type 3) and handset which predates the use of tritium luminous compound. Dials were often exchanged during routine service, making this a rare survivor. and indeed it's in great condition. The watch has the correct matching 1961 date coded bracelet. 

Vintage Rolex watches are all about the details and as is often the case some components have been replaced during the life of this watch. The end links on the bracelet are a later type (type 580 rather than the correct type 58); the lume plots on both dial and hands have certainly been redone at some point; the case has been polished, although this has been done sympathetically. The bezel ring is a later service replacement (the milling on the sides is a slightly different form from the original that would have come with the watch), and the bezel insert is rather faded on the blue side and I think this is also a later service replacement. 

The watch came to me with a Rolex chronometer certificate and box, although this isn’t the original certificate for this watch (it’s for a different serial number movement), I’ve included it since it’s from the correct period and the box is always a handy thing to have!

An eminently wearable example of the Rolex GMT for the discerning collector and indeed for someone with the patience to source the correct bezel and insert this could be really the centrepiece of any collection. 

Case diameter: 39mm
Case material: stainless steel
Strap width: 20mm
time keeping: grade A