Think you will find was a Naval Store carrier, all small PSTOn craft were given the letter c followed by a number right up until Port Auxiliary was came into being the oil depot tugs were known by a C and a number until P.A.S came into being and the tugs were then given a name. I used to have a pic of one called C99, all the larger store carriers pre war were c plus a number though the Naval Armament carriers were all named as were their tugs . I believe Mountfleet do a model of one which is called C635 I believe,
