Omega Speedmaster in 1957, but until 1968, the 321 movement was replaced by the 861 movement. The 861 movement is the predecessor of today’s 3861 movement. Compared with the 321 movement, the 861 movement has some structural improvements. For example, its cylindrical wheel was changed to a cam, and the Y-shaped splint was changed to a whole piece. So the 861/1861/3861 family, in terms of status, is lower than the 321 movement.
From 1968 to 2018, in the middle 50 years, Omega never used the 321 movement again. One of the main reasons is the copyright issue of the movement. Because the 321 movement was jointly developed by Omega and Lemania, the Lemania replica watches factory flew solo and was merged into Breguet in 1981. Breguet went through several twists and turns and joined the Swatch Group. Although Omega and Breguet are both of the Swatch Group, the copyright of the 321 movement falls under the name of Breguet. After that, Omega finally obtained the copyright of the 321 movement again. Therefore, it was not until 2019 that the Omega Speedmaster 321 came back.