In 1944 Kelly Johnson's design team managed to get the jet fighter P-80 Shooting Star in the air just 143 days after the initial design process started. Try doing that these days!
Also in 1944, Germany's last ditch efforts at fighter jets outdid Lockheed with the Heinkel He 162. Hermann Goering and Albert Speer decided that the answer to mounting losses was to have a fighter that was so cheap it could be thrown away if damaged or worn out. Designed to be easy to fly, cheap, fast and mostly wooden, this jet's requirements were put together by September 10 1944, and by September 25 Heinkel's design was the winner. Only a couple months later, on December 6 the first prototype was flying.
January 1945 already saw the first 46 production aircraft delivered to the test flying evaluation group, and the next month deliveries were headed to the actual operations group JG/1. By the end of the war in May, over 120 had already been delivered to fighting units, 200 more were completed and waiting to be transferred plus 600 more were being built but not yet complete. A remarkable bit of engineering brought on by desperation. A production rate of 1,000 per month was called for, which was achievable - finding the pilots was the real problem by that stage of the war.
Top speed at 20,000 feet was 562 mph. on emergency power and it could reach 39,000 feet in altitude.
It doesn't even look that out of date all these years later.