If Shimano was in two minds about derailleurs before 1967, that all changed with the Shimano Skylark. Shimano took the geometry of the Simplex Export 61, tweaked it slightly and avoided Simplex’s fatal mistake of manufacturing it in plastic. The result was the Skylark - and it went on to be a best seller.
Shimano referred to the Skylark as having a ‘Servo-Pantagraph’ design (or sometimes a ‘Servo-Panta’ design (?!?)). I never knew quite what this meant - a ‘servo’ system surely has to incorporate a feedback mechanism - but I have always guessed that it means that the derailleur has two sprung pivots. Perhaps the position of the pulley cage generates ‘feedback’ by repositioning the parallelogram. Perhaps it just means ‘buy me’.
Over the years (all 40 of them) Shimano has added features and then taken them away again:
In many ways the most recent Tourney derailleurs in this collection are most similar to the very original Skylarks. It is perfectly reasonable to regard today’s Tourneys as Skylarks with different cosmetics.
I cannot claim that Skylarks, Larks, Eagles or Tourneys are the sexiest of derailleurs. Most derailleur collectors couldn’t be less interested in them - but they were Shimano’s first big selling model, led to Shimano’s breakthrough into the USA and Shimano has made them in their millions. Even more importantly Taiwanese, Chinese and Indian manufacturers have copied them and produced their copies in their tens of millions.
As I say in my piece on Shimano; when the world changes gear - it uses a Skylark.
Shimano RS (RS12) 1981?