Meanwhile, Seversky's AP-4 continued in development, finally going into production as the P-43 Lancer. 272 P-43s were eventually produced, with 108 of them being sent to China to be used against the Japanese. Many passed through the hands of the AVG Flying Tigers, whose pilots were pleased with the plane's performance at altitudes up to , while their P-40s were ineffective at altitudes over . Perhaps Claire Chennault disliked the early P-43's lack of self-sealing fuel tanks and armor. He declined to retain the plane for his crews.