Hi My mother was born in Tack's Beach, Placentia Bay, Newfoundland. My mother's brother Maxwell James Penney did serve in the Korean war. He returned home and went back to the war. Maxwell died in 2004.
During war times it is difficult to tell if they used major cities, such as St. John's, instead of specific towns given some towns were quite small.
I am not sure if this is the M.J. Penney that your mum used to visit.