SSIH soon became a major player in the Swiss watchmaking industry. In 1948, the centenary of Omega, the SSIH employed 1,600 people and produced over 500,000 watches. In the years that followed, SSIH grew steadily: 3,000 employees in the early 1960s, over 7,000 in the early 1970s, and over 10 million pieces produced. This growth was also, and above all, the result of company takeovers: Marc Favre in 1955, Eigeldinger et Cie. in 1957, Rayville S.A., manufacturer of Blancpain watches in Villeret in 1961. It should be noted that the SSIH was interested in Rayville's remarkable ladies' calibres, not the Blancpain brand, which was quickly buried. Also in 1961, Rayville acquired the Cortébert industrial site, and in 1965, the Langendorf Watch Company, manufacturer of Lanco watches.
At the end of the 1960s, when SSIH had to compete with Timex and Seiko in the economic watch sector, it acquired Aetos, a major manufacturer of anchor watches, in 1969, and two years later ESTH (Economic Swiss Time Holding created in 1967), the largest Swiss manufacturer of Roskopf watches (Buler, Continental, Ferex brands, etc.). The takeover of Hamilton, between 1971 and 1974, was seen as indisputable proof of the supremacy of Swiss industry over its American counterpart.