Cat.IIIC operations -
There are no Cat.IIIC operations anywhere in the world -
In the 1970s, there were some attempts to have them in UK and France - I think with Tridents and Caravelles - also in France for the "Postale de nuit" (night air mail flights) -
Some 747-200/300 I used to fly were certificated for Cat.IIIA but were fully capable of Cat.IIIB operations - yet most airlines operating them downgraded the Cat.IIIA capability, to Cat.II in view of maintenance and training costs -
In 20 years of operations with 747, I had only 1 (I say again, one) Cat.IIIA ILS approach - all other instances, Cat.II was sufficient -