But both the P-61A and P-61B were felt to have a deficiency in top speed and operational service ceiling. To improve the performance, two new more powerful Pratt & Whitney R-2800C engines were applied. With this increase in power, the top speed and altitude were increased to 430 mph and 30,000 feet.
Another change on the P-61C was the wide chord propellers and special “fighter brakes” which allow the P-61C to turn much tighter and avoid overshooting targets.