[Station X]

M4 machines as used in U boats used a special thin non-revolving rotor fitted next to the reflector. It could only be turned manually when setting up the machine and then remained stationary. The remaining three rotor positions could each be fitted with one of eight rotors.

One position of the non-revolving rotor made it compatible with three rotor machines.

I don't know whether the fourth rotor in the Spanish machine revolved automatically or not. If it revolved automatically it would only have revolved infrequently when coding or decoding a message and in most cases not at all.