One of the earliest operations research groups during World War II was conducting a study on the optimum utilisation of Spitfire and Hurricane aircraft during the Battle of Britain. Whenever one of these planes returned from battle, the locations of the bullet holes on it were carefully plotted. By repeatedly recording these data over time and studying the clusters of data, the group was able to estimate the regions of the aircraft most likely to be hit by enemy gunfire, with the objective of reinforcing these regions with specin' armour. Choose the correct answer below. What difficulties are involved with this study? The locations of bullet holes may not be precise due to the need for repairing aircraft so they could be sent up again. The locations of bullet holes may change if the enemy changes tactics. Reinforcing these regions of the aircraft would make it more challenging to record the locations of bullet holes in the future. The study was only observing planes that returned safely. Planes that were shot down could not be analysed.