blomman Mr Blue
38586
Welcome here!
Yes, in the early 1950s Cartier branded several different JLC models with their name.
Among them the Memovox.
Yours looks like the JLC reference 3151 with the Cal 489 inside.
Not sure if this was only in the US or if Cartier did it worldwide.
Do you know where your grandfather bought his watch?
A very nice watch, worth to give it some love!
Best
Blomman