The Omega 321 caliber is the evolution of the 27 CHRO C12 born in 1942, it have been designed by the famous watchmaker Albert Piguet. In 1942 it was the smallest chronograph movement ever made

The number 27 indicates the diameter of the caliber : 27 mm, CHRO is the abreviation of "chronograph" and C12 indicates that the watch has a 12 hour counter (an uncommon feature at this time)

In 1946 the 27 CHRO C12 evolve with minor changes and is renamed Omega 321

Its robust components, produced with maximum precision, not only offered perfect interchangeability whitout modification, which was highlty unusual at the time for such an instrument, they were also appreciated by master watchmakers and collectors.

this calibre equipped the Speedmaster chosen by NASA for its first manned spaceflight missions and, furthermore, for the first extra-vehicular activity in outer space, incoluding on the Moon (see NASA part of this website). More than 40 000 units of the Omega 321 caliber have been produced.

After the huge sucess of the Speedmaster in the end of the 60’s Omega decided to introduce on the market a simplified version of the caliber 321 also designed by Albert Piguet : the Omega 861. the Omega 321 was more than 20 years old and it was time to simplify its construction for mass production : the Speedmaster have been equiped with the 861 movement in 1968 :

1°) the column whell mechanism have been replaced by a cam system simplifying the assembly of the movement

2°) a nylon pusher is introduced in the movement , which need no lubrification and easy to produce

3°) a flat spiral glucidur replace the Breguet spiral and the beat change from 18000 bph to 21600 bph

On the industrial point of view this was a right decision and a huge sucess : more than 300.000 861 movements have been produced so far , and the movement is still in production

but on the collectible point of view many of my fellow collectors and myself will regret the move …

Interesting note concerning "the moon watch" :

The Omega speedmasters engraved "the first watch on the moon" are fitted with 861 movements , and the previous models have only the sea monster logo : anybody might think viewing thoses backs that the speedmasters fitted with the 861 are "the moon watch"

In fact NASA qualification took place in 1965 at this time the 861 movement was not available and the purchasing for the astronauts speedmasters where bought before the 861 introduction. So the Speedmasters of Apollo missions which goes on the moon where not equipped with 861 movement

Very curiously Speedmasters fitted with "the first watch on the moon" engraving are NOT the moonwatches , the previous ones without the engravings ARE the moonwatches ! , refer to the NASA section of this site for more details