The PA46 pilot stated that he was stopped on the taxiway behind another airplane when a P51 collided with his airplane from behind. After the collision, the P51 pilot reported to the PA46 pilot that he did not see the PA46. The P51 pilot stated that he was taxiing to the runway and was aware of two other airplanes taxiing ahead of him. He stated that he was “[taxiing] at idle speed, making long S turns, and making sure to clear all aircraft ahead.” The first airplane in line departed and he continued taxiing toward the runup area and was unaware that the second airplane was stopped on the taxiway. The P51 collided with the empennage of the PA46 and the pilot applied the brakes to stop the airplane. The pilot reported that there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation. The PA46 sustained substantial damage to the empennage.