Query: To mitigate the loses of the B-29, what did the US Air Force do?
Context: They were fast enough to dive past the fighter escort of P-80 Shooting Stars and F9F Panthers and could reach and destroy the U.S. heavy bombers. B-29 losses could not be avoided, and the Air Force was forced to switch from a daylight bombing campaign to the necessarily less accurate nighttime bombing of targets. The MiGs were countered by the F-86 Sabres.