Original sentence: The P-40 initially proved quite effective against Axis aircraft and contributed to a slight shift of momentum in the Allied favor
Edited sentence: According to some sources  it initially proved quite effective against Axis aircraft and contributed to a slight shift of momentum in the Allied favor.Like the Bell P-39 Airacobra, it was mediocre at high altitude.The Curtiss P-40 was never an outstanding aircraft.The P-40 was never an oustanding aircraft