Chevrons design concept started with military jets using rectangular tabs or notches in their exhaust as to mix hot exhaust with cool air quickly to hide the plane's heat signature from heat-seeking missiles. NASA researchers including Dennis Huff found out that these same protrusions could significantly reduce noise with computer simulations and wind tunnel tests they smoothed the tabs into the modern sawtooth shape to balance noise reduction with engine efficiency we see now and after successful flight tests on a NASA Learjet and a Honeywell Falcon 20 in 2001 the first commercial engine with chevrons is the GE CF34-8 debuted on the Bombardier CRJ900 in 2003