I came across that thing by accident. I had been watching old Dick Tracy serials from the 1940’s and saw the Captain Marvel serial. It was about 3.5 hours long and I decided to watch it.
I got a real kick out of it, of course the special effects were primitive, reminded me of watching early Dr. Who stuff, but it was all in good fun.
I love watching 1930’s and 40’s movies, the men look like men and the women are real women, nothing fake about those gals and they were pretty good actress’ also for B and C types.
There is a long Green Hornet serial and one called The Spider I think on YT.
Not bad for their time.