Even though Dad went through the shenanigans of "becoming" Catholic, I suspect he did it because he wanted to be buried next to Mom. This said knowing that Dad's mother, who took her own life in 1922 when Dad was 11, is buried in an unmarked grave in Camp Verde, AZ.
I'm not too sure Dad believed when I was a child and maybe not when I was a teenager. We never talked about it. All I know is my father's relationship with me changed after I'd "proved myself" in the USN. Then Mom had her first brain tumor surgery (back when it was a lot more barbaric than the barbarity of now) and Dad just gave up. That's when the interest in converting started.
Made it very weird at the RC funeral mass, sitting in the front row knowing that I couldn't believe what I was hearing & the premises of what was said. I think that was the beginning of my coming out, finalized two years later when Mom died. (She had an outfit in her closet with a note pinned to it that said "For Jesus," meaning she wanted to be buried in it, which she was, right next to Dad in an RC-approved cemetery.)
And no, I know Dad never knew that I was a disbeliever. Might might have thought of it but aphasia prevented her from saying much. I don't mince words about it now. Like Dad used to say with a wave of the hand, as if fanning away ghosts, "Chinga'o. Así sea."