On July 17 , 1944 , napalm incendiary bombs were dropped for the first time by American P-38 pilots on a fuel depot at Coutances , near St. LÃ , France . On July 17 , 1944 , napalm incendiary bombs were dropped for the first time by 14 American P-38 Lightning aircraft of the 402d Fighter Squadron \/ 370th Fighter Group on a fuel depot at Coutances , near St. LÃ , France .