Great ideas! Thanks to all who contributed. I think (hope) my tub is some kind of plastic or acrylic. Maybe it's as easy as sawing it up. I do have a big pick ax, in case it's iron tub.
This was what I was trying to get: the big way is to just saw 'em up to get 'em out.
Other good ideas included, too. Thanks.
Don't try to do it with a sledge hammer, use a pick. One of the older kind with plenty of heft. Even if you have to rent one. I had an old (1955) tub reduced to pieces small enough to put one in my pocket in less than an hour.
Doing it with a sledge hammer just caused the sledge to bounce. Doing it with the pick caused a small hole and a crack line, and I followed the crack lines.
And I replaced it with a 5 ft shower base, with two seats. But that's another story.
Many years can cause some sag in the floor wood. Suggesting you put a level to it, and if it's a bit uneven, you bring up the base with some cement board, with fresh, wet grout under it. And more fresh cement without stone aggregate when you put the shower base in. That way, the water will always drain correctly, and when you're in it, the floor will be LIKE A ROCK.
Hey, do it right, insulate the walls with Styrofoam so it won't be cold in the winter, and if there's a window, replace it with glass block. Just some suggestions, as applicable.