The Second World War marked the universal acceptance of the integration of air power into combined arms warfare. Although the German "Luftwaffe" was the only force to use CAS at the start of the war, all the major combatants had developed effective air-ground coordination techniques by the conflict's end. New techniques, such as the use of forward air control to guide CAS aircraft and identifying invasion stripes, also emerged at this time, being heavily shaped by the Italian Campaign and the invasion of Normandy. CAS practices continued to advance in further conflicts, including the Korean War and the Vietnam War; major milestones including the introduction of attack helicopters and the creation of aerial gunships, such as the Bell AH-1 Cobra and the Douglas AC-47 Spooky. While many CAS aircraft have been propeller driven, several jet aircraft, such as the A-10 Thunderbolt II ("Warthog") and the Su-25 ("Frogfoot"), have been developed as well.