 Both the United States and Japan stepped up the training of aircrew , but the United States had a more effective pilot rotation system , which meant that more veterans survived and went on to training or command billets , where they were able to pass on lessons they had learned in training rather than in combat , where errors were more likely to be fatal . By the time of the Battle of the Philippine Sea in June 1944 , the Japanese had nearly rebuilt their carrier forces in terms of numbers , but their planes , many of which were obsolescent , were largely flown by inexperienced and poorly trained pilots . 
