In 1960, Nikon introduced a camera for continuous recording.
It was Nikon S3M. When mated with a S72 motordrive unit,
it takes 6 half-frames/sec. But the users didn't find it much of an
advantage to the 4 full frames/sec. of the Nikon F with the F36 motor drive.
Thus the last of the Nikon RF series didn't sell well and only 195 units
were produced and made this camera a collectors' dream.

From the front, it looks just like another S3, except for its 660 series
serial number and the film counter up to 72 shots. note the red mark at the 40th.

But once if you viewed from the back, and the back removed, you can't mistake
the half-frame aperture and the unique frame selector lever.

The frame selector lever selects from a 3.5cm, a 5cm and a 10.5cm frame.
The die-cast body is unique to this model. It looks to be made for this model only.

And from the bottom, you can see the coupling plate for the motor drive.

Though all the S3M's are designed to use with motor drives(hence S3M(motor)),
majority of the S3M were sold without a motor and found without a motor today.

Once again take a look from the front with the shutter wide open.

S3M user's manual(Japanese version)