Tne rangefinder speed monster Nikkor-N 5cm f/1.1 was launched in its time to complement the capabilites of the Nikon SP and S3 presumably. The first version used the same internal mount and through-the-camera focussing as all the other 5cm lenses, however it was so heavy that this operation became less than smooth and in fact might damage the camera. Thus Nikon made a second version with external mount instead, whic is the one I now own.
The lens is quite elusive as the production numbers were small at the time and asking price nowadays is pretty steep.