Subfloor for 5″ x 3/4″ White Oak Hardwood

The subfloor in the house is currently 1/2″ Plywood. I think the min recommended plywood subfloor is 5/8″ ply I believe. If that is the case I could add another layer as underlayment. Obviously want to keep the height to a min so not sure if 1/4″ or 1/2″ would be suitable.
I can either add more nails or screw down the existing 1/2″ subfloor to the joists. Is screwing prefered over the spiral flooring nails?
Replies
Building techniques have changed over the years. Sub flooring went from 3/4" boards to 1/2" plywood during the 60's. At that time, hardwood flooring wasn't very popular. Wall to wall carpet and vinyl were the norm until the late 70's, 5/8" underlayment, often particle board, was used under carpet and 5/8" plywood used under vinyl, making for a two ply floor over the 1/2" subfloor. Many homes have 3/4" hardwood over 1/2" plywood subflooring and I don't know of any issues. More important is the floor framing. Adding a layer won't make up for inadequate framing. With 16" centers on the joists and adequate depth of the joists for the span, you will be fine, tile is another matter.
Screws
Screw the 1/2" subfloor down as needed.
Lay down some felt paper (or rosin paper).
Chauk lines directly over the floor joists and always nail the oak flooring over the joists (you can also put some into the subfloor as needed, but they won't have the same grip).
I have woked on many an old house that had no subfloor, just the strip flooring nailed directly to the joists.
If you really feel the need for a thicker sub floor, add 5/8 or 3/4"
Terry