Association of Dunkirk Little Ships

I am attempting to put the "meat on the bones" of a man who remarked on a very few occasions in his life about serving in the evacuations at Dunkirk. His name was Joseph Sheriff Devlin, and he would have been in his late 30's. Joseph Devlin often served aboard the Clyde Steamers and made reference in the few times mentioned of the protection offered by the vessel he was aboard, in that it had a steel mail room; To date, we have attempted to contact the Cal-Mac historian, as well as searched the high and low of the National Archives. Is there anyone who can identify the involvement of the steamers? Any familiarity or contact with Joseph? Being that he had connections to the port as a resident of Greenock, we are hoping his references and posting some threads might help rebuild his history for the family. He passed away in 1976, his wife Jessie, in 1986. Any direction or assistance would be greatly appreciated in identifying his participation with the evacuations as well as any knowledge to his merchant marine service.