What do I know about the Rapid brand? Not much:
- It was manufactured in Milano, Italy - and is not to be confused with the French 'Super Rapid' brand.
- In 1945 a Bruno Terzi patented a design for a 3-speed derailleur operated by back pedalling.
- Around 1946 Rapid released a version of this derailleur. Le Cycle describes this as a 4-speed system that is operated by back pedalling a quarter of a turn of the chainset. How exactly this worked in the intermediate gears is still unclear to me.
- Around 1949 Rapid released a second, rather advanced, parallelogram derailleur that mounted underneath the chainstay. This derailleur was controlled by a conventional cable. Note that this was an Italian parallelogram derailleur released several years before the Campagnolo Gran Sport.