The KC-135 was derived from the 1950s prototype Boeing 367-80 - known colloquially as the 'Dash 80' - which also spawned the highly successful Boeing 707 airliner. The US Air Force harnessed the basic design for military use as an air-to-air refuelling tanker, and in doing so began the KC-135 story. Although it was first introduced to service with the United States Air Force in 1957, a continued stream of development and upgrade programmes have kept it 'current' in an ever changing and technologically advanced world. Whilst a replacement is planned, the contemporary KC-135R model continues to be operated in large numbers by US units and has the potential to continue for some years to come. Wider afield, countries such as Chile, France, Singapore and Turkey also utilise versions of type, making it a regular participant in NATO and other international exercises and operations around the globe.