The term “ducktail” can probably be traced back to the Porsche sales department, which initially did not take to the spoiler and regarded the 911 Carrera RS 2.7 as all but unsalable. What they said, not meaning to be kind, was, “It looks like a duck’s tail.” First presented at the 1972 Paris Motor Show, the RS was the crowning achievement in the history of the 911 series: the first car to make use of aerodynamic aids and the first car since the 356 to carry the legendary Carrera name. The trade journal auto motor und sport was impressed: “The fastest German series-production car with 210 hp under the hood and, thanks to the tail on the rear, looks so distinctive that no one will ever have the slightest doubt as to what car is driving in front of them.”
The FIA Group 4 rules that governed top tier GT racing at the time allowed engines to be bored out but only to the capacity limit of the car’s class. That meant the 1972 2.4S could be bored out to the 2.5 litre class limit but no further. The first thing Porsche needed for their 1973 model line-up was a 911 with an engine bigger than 2.5 litres. This time, Group 4 GT racing was Porsche’s target, and it needed an up to snuff 911 to take on all comers. To keep the FIA happy Porsche had to produce at least 500 of them for the road. Of course, the road and race cars had to be related, so some fairly drastic measures were taken on the road car to ensure it would match its racier sibling. 
1580 Carrera RS’ hit the road, so the FIA was happy to let the Carrera RS go racing. But the 2.7 RS wasn’t the end of the story – a 3.0-litre car with more power came out later with a chassis similar to that of the ’73 Carrera RSR and brakes from a 917 race car.