I had a quick look through the reports but didn't see if these test were related with the new jet fighters that were coming on line about then. Would you know why they were testing this type of tail Jon ?
The first line in the advance report:
The NACA is conducting flight tests of an all-movable horizontal tail installed on a Curtiss XP-42 air-
plane because of its possible advantages as a longitudinal control for flight at high Mach numbers.The NACA's research of this sort was general rather than specific, and as the program started during
the war it's doubtful it had anything to do with any particular design, and probably there wasn't any
likelihood of incorporation into existing
jet fighter designs, but the results were possibly used
during X-2 development.