1975 Omega Speedmaster Automatic (Ref. 176.0012) "Mark 4.5"

With the immense success Omega saw from the Speedmaster Professional series, especially after its iconic trip to the moon, they decided the expand the Speedmaster model with the ever-evolving Mark series of chronographs. The Mark II debuted in 1969 with a bold, sunburst-finished tonneau-style case. The Mark III was introduced in 1971 and was the first Speedmaster to employ an automatic winding movement using the Lemania cal. 1340. The Mark IV was introduced in 1973 and melded the Mark II case style with the same Lemania-based movement of the Mark III. After a short hiatus, Omega created the Mark V, which featured a very evolved aesthetic that many refer to as 'futuristic'.

So what is a Speedmaster Mark 4.5? The ref. 176.0012, also known as the"Mark 4.5", is the unofficial name of the Speedmaster Automatic that bridges the gap between the Mark IV and the Mark V. This model employs a very similar case to the Mark IV but employs the same movement as the Mark V, the Lemania cal. 5100. Interestingly, the Mark 4.5 was manufactured for the longest period out of the actual models in the Mark Series, from 1974 to 1986.