The convergent nozzle was replaced with a C-D nozzle on the same engine J57 in the same aircraft F-101. The increased thrust from the C-D nozzle (2000 lb at SL TO) on this engine raised the speed from Mn=1.6 to almost 2.0 enabling the Air Force to set a world's speed record of 1207.6 mph which was just below Mn=2 for the temperature on that day. The true worth of the C-D nozzle was not realised on the F-101 as the intake was not modified for the higher speeds attainable.