Thank you all again.
I've been looking for in some spanish press archives and I found that the first SSR equipments (for civil aviation) in Spain were installed in 1972. I found some old brochures from the early 60's (from outside of Spain, from BEA for example) saying that their aircrafts were fitted with new “transponder equipments”. This thing makes me think that in other european countries SSR equipments were installed maybe since the early 60's or late 50's. (?)
The aircraft's transponder equipment by those times was only linked with the SSR, or it had already another kind of functions?