Could the 1921 trials have used a radio-controlled target ship?
Short answerNot for the purpose of these tests. They measured weapon damage, while a moving radio-controlled target would test the crews' ability to hit a ship.
NotesA radio-controlled ship would be useful for gunnery practice or aircrew training against moving targets. These trials were intended to assess the damage caused by weapons. Inspectors needed a target they could examine after it was hit, and movement added nothing essential to that task. The stationary setup therefore suited the experiment, although it did not reproduce combat against a maneuvering warship.